Attach a variable scheme to an instrument using a custom field, and register only the instrument in a transaction

snippet.cs

            var client = new RestRepositoryClient(info);

            VersionableBase.DefaultAgencyId = "int.example";
            MultilingualString.CurrentCulture = "en";

            var instrument = new Instrument();
            var varset = new VariableScheme();
            var customField = new CustomField();
            customField.RelatedItemIdValue = new TypedIdTriple(varset.CompositeId, DdiItemType.VariableScheme);
            customField.ValueType = CustomFieldType.Relationship;
            customField.Title.Current = "variables";
            instrument.CustomFields.Add(customField);

            var transaction = await client.CreateTransactionAsync();

            RepositoryTransactionAddItemsRequest addItemsRequest = new RepositoryTransactionAddItemsRequest();
            addItemsRequest.TransactionId = transaction.TransactionId;
            var item = VersionableToRepositoryItem(instrument);
            addItemsRequest.Items.Add(item);
            transaction = await client.AddItemsToTransactionAsync(addItemsRequest);

            RepositoryTransactionCommitOptions options = new RepositoryTransactionCommitOptions();
            options.TransactionId = transaction.TransactionId;
            options.TransactionType = RepositoryTransactionType.CommitAsLatestAndPropagateVersions;

            var result = await client.CommitTransactionAsync(options);