RenderingConfigFactory.cs

public interface IRenderingConfigFactory
{
    IRenderingConfiguration Create<T>(IRenderingConfiguration renderingConfig, T itemSerializer) where T : class, IItemSerializer;
}

public class RenderingConfigFactory : IRenderingConfigFactory
{
    public IRenderingConfiguration Create<T>(IRenderingConfiguration renderingConfig, T itemSerializer) where T : class, IItemSerializer
    {
        return new DefaultRenderingConfiguration
        {
            IncludeServerUrlInContextItemMediaUrls = renderingConfig.IncludeServerUrlInContextItemMediaUrls,
            ItemSerializer = itemSerializer, // Custom item serializer
            Name = renderingConfig.Name,
            PlaceholdersResolver = renderingConfig.PlaceholdersResolver,
            RenderingContentsResolver = renderingConfig.RenderingContentsResolver,
        };
    }
}