ODataQueryOptionExtensions - Modifying ODataQueryOptions on the fly - https://d-fens.ch/2017/02/26/modifying-odataqueryoptions-on-the-fly/

## ODataQueryOptionsExtensions.cs
/**
 * Copyright 2017 d-fens GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Web.Http.OData.Query;

namespace Net.Appclusive.WebApi.OdataServices
{
    public static class ODataQueryOptionsExtensions
    {
        public static readonly ODataQuerySettings _OdataQuerySettings = new ODataQuerySettings();

        public static ODataQueryOptions Transform
        (
            this ODataQueryOptions queryOptions,
            ODataQueryOptionsUtilitiesTransformSettings transform
        )
        {
            return ODataQueryOptionsUtilities.Transform
            (
                queryOptions,
                transform
            );
        }

        public static ODataQueryOptions Transform
        (
            this ODataQueryOptions queryOptions,
            Func<IReadOnlyDictionary<string, string>, FilterQueryOption, string> transformFilter,
            Func<IReadOnlyDictionary<string, string>, OrderByQueryOption, IList<string>> transformOrderBy,
            Func<IReadOnlyDictionary<string, string>, SelectExpandQueryOption, IList<string>> transformExpand,
            Func<IReadOnlyDictionary<string, string>, SelectExpandQueryOption, IList<string>> transformSelect,
            Func<IReadOnlyDictionary<string, string>, SkipQueryOption, int?> transformSkip,
            Func<IReadOnlyDictionary<string, string>, TopQueryOption, int?> transformTop
        )
        {
            Contract.Requires(null != queryOptions);

            return ODataQueryOptionsUtilities.Transform
            (
                queryOptions: queryOptions,
                transformFilter: transformFilter,
                transformOrderBy: transformOrderBy,
                transformExpand: transformExpand,
                transformSelect: transformSelect,
                transformSkip: transformSkip,
                transformTop: transformTop
            );
        }

        public static ODataQueryOptions RemoveSkipCount(this ODataQueryOptions queryOptions)
        {
            Contract.Requires(null != queryOptions);
            Contract.Ensures(null != Contract.Result<ODataQueryOptions>());

            return ODataQueryOptionsUtilities.Transform
            (
                queryOptions,
                new ODataQueryOptionsUtilitiesTransformSettings
                {
                    Skip = (map, option) => default(int?)
                }
            );
        }

        public static ODataQueryOptions SetSkipCount(this ODataQueryOptions queryOptions, int value)
        {
            Contract.Requires(null != queryOptions);
            Contract.Requires(0 <= value);
            Contract.Ensures(null != Contract.Result<ODataQueryOptions>());

            return ODataQueryOptionsUtilities.Transform
            (
                queryOptions,
                new ODataQueryOptionsUtilitiesTransformSettings
                {
                    Skip = (map, option) => value
                }
            );
        }
    }
}

## ODataQueryOptionsUtilities.cs
/**
 * Copyright 2017 d-fens GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics.Contracts;
using System.Linq;
using System.Text;
using System.Web.Http.OData.Query;
using biz.dfch.CS.Commons.Linq;
using Net.Appclusive.Public.Domain;

namespace Net.Appclusive.WebApi.OdataServices
{
    public class ODataQueryOptionsUtilities
    {
        public const char QUERY_OPTIONS_PREFIX = '?';
        public const char QUERY_OPTIONS_SEPARATOR = '&';
        public const char QUERY_OPTIONS_DELIMITER = '=';
        public const string QUERY_OPTION_EXPAND = "$expand";
        public const string QUERY_OPTION_SELECT = "$select";
        public const string QUERY_OPTION_SKIP = "$skip";
        public const string QUERY_OPTION_TOP = "$top";
        public const char QUERY_OPTION_SELECT_EXPAND_DELIMITER = ',';

        public static ODataQueryOptions Transform
        (
            ODataQueryOptions queryOptions,
            ODataQueryOptionsUtilitiesTransformSettings settings
        )
        {
            Contract.Requires(null != queryOptions);
            Contract.Requires(null != settings);
            Contract.Ensures(null != Contract.Result<ODataQueryOptions>());

            return Transform
            (
                queryOptions: queryOptions,
                transformFilter: settings.Filter,
                transformOrderBy: settings.OrderBy,
                transformExpand: settings.Expand,
                transformSelect: settings.Select,
                transformSkip: settings.Skip,
                transformTop: settings.Top
            );
        }

        public static ODataQueryOptions Transform
        (
            ODataQueryOptions queryOptions,
            Func<IReadOnlyDictionary<string, string>, FilterQueryOption, string> transformFilter,
            Func<IReadOnlyDictionary<string, string>, OrderByQueryOption, IList<string>> transformOrderBy,
            Func<IReadOnlyDictionary<string, string>, SelectExpandQueryOption, IList<string>> transformExpand,
            Func<IReadOnlyDictionary<string, string>, SelectExpandQueryOption, IList<string>> transformSelect,
            Func<IReadOnlyDictionary<string, string>, SkipQueryOption, int?> transformSkip,
            Func<IReadOnlyDictionary<string, string>, TopQueryOption, int?> transformTop
        )
        {
            Contract.Requires(null != queryOptions);
            Contract.Ensures(null != Contract.Result<ODataQueryOptions>());

            var uri = queryOptions.Request.RequestUri;
            var queryParameters = uri.Query
                .TrimStart(QUERY_OPTIONS_PREFIX)
                .Split(new[] { QUERY_OPTIONS_SEPARATOR }, StringSplitOptions.RemoveEmptyEntries)
                .ToDictionary
                (
                    e => e.Split(QUERY_OPTIONS_DELIMITER).FirstOrDefault(),
                    e => e.Split(QUERY_OPTIONS_DELIMITER).LastOrDefault()
                );

            if (null != transformFilter)
            {
                var result = transformFilter(new ReadOnlyDictionary<string, string>(queryParameters), queryOptions.Filter);
                if (null != result)
                {
                    queryParameters[QUERY_OPTION_EXPAND] = result;
                }
            }

            if (null != transformOrderBy)
            {
                var result = transformOrderBy(new ReadOnlyDictionary<string, string>(queryParameters), queryOptions.OrderBy);
                if (null != result)
                {
                    queryParameters[QUERY_OPTION_EXPAND] = string.Join(QUERY_OPTION_SELECT_EXPAND_DELIMITER.ToString(), result);
                }
            }

            if (null != transformExpand)
            {
                var result = transformExpand(new ReadOnlyDictionary<string, string>(queryParameters), queryOptions.SelectExpand);
                if (null != result)
                {
                    queryParameters[QUERY_OPTION_EXPAND] = string.Join(QUERY_OPTION_SELECT_EXPAND_DELIMITER.ToString(), result);
                }
            }

            if (null != transformSelect)
            {
                var result = transformSelect(new ReadOnlyDictionary<string, string>(queryParameters), queryOptions.SelectExpand);
                if (null != result)
                {
                    queryParameters[QUERY_OPTION_SELECT] = string.Join(QUERY_OPTION_SELECT_EXPAND_DELIMITER.ToString(), result);
                }
            }

            if (null != transformSkip)
            {
                var result = transformSkip(new ReadOnlyDictionary<string, string>(queryParameters), queryOptions.Skip);
                if (result.HasValue)
                {
                    queryParameters[QUERY_OPTION_SKIP] = result.Value.ToString();
                }
                else
                {
                    if (queryParameters.ContainsKey(QUERY_OPTION_SKIP))
                    {
                        queryParameters.Remove(QUERY_OPTION_SKIP);
                    }
                }
            }

            if (null != transformTop)
            {
                var result = transformTop(new ReadOnlyDictionary<string, string>(queryParameters), queryOptions.Top);
                if (result.HasValue)
                {
                    queryParameters[QUERY_OPTION_TOP] = result.Value.ToString();
                }
                else
                {
                    if (queryParameters.ContainsKey(QUERY_OPTION_TOP))
                    {
                        queryParameters.Remove(QUERY_OPTION_TOP);
                    }
                }
            }

            var newQueryOptions = new StringBuilder();
            queryParameters.ForEach(e =>
            {
                newQueryOptions.Append(QUERY_OPTIONS_SEPARATOR);
                newQueryOptions.Append(e.Key);
                newQueryOptions.Append(QUERY_OPTIONS_DELIMITER);
                newQueryOptions.Append(e.Value);
            });

            queryOptions.Request.RequestUri =
                new Uri($"{uri.Scheme}://{uri.Authority}{uri.AbsolutePath}{QUERY_OPTIONS_PREFIX}{newQueryOptions}");

            var newOdataQueryOptions = (ODataQueryOptions)Activator.CreateInstance(queryOptions.GetType(), queryOptions.Context, queryOptions.Request);

            return newOdataQueryOptions;
        }
    }
}

## ODataQueryOptionsUtilitiesTransformSettings.cs
/**
 * Copyright 2017 d-fens GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Collections.Generic;
using System.Web.Http.OData.Query;

namespace Net.Appclusive.WebApi.OdataServices
{
    public class ODataQueryOptionsUtilitiesTransformSettings
    {
        public Func<IReadOnlyDictionary<string, string>, FilterQueryOption, string> Filter;
        public Func<IReadOnlyDictionary<string, string>, OrderByQueryOption, IList<string>> OrderBy;
        public Func<IReadOnlyDictionary<string, string>, SelectExpandQueryOption, IList<string>> Expand;
        public Func<IReadOnlyDictionary<string, string>, SelectExpandQueryOption, IList<string>> Select;
        public Func<IReadOnlyDictionary<string, string>, SkipQueryOption, int?> Skip;
        public Func<IReadOnlyDictionary<string, string>, TopQueryOption, int?> Top;
    }
}