Is there a way to disable certain features provided by Railcraft? For example, I do not want to be able to get more rails for the same amount of resources, since I want to keep the values as much vanilla as possible.
Forge does not provide any way to disable part of a mod. You can only enable or disable a mod that way. Your best option is to edit the source code of the mod which will therefore require knowledge in Java. There are many tutorials for coding minecraft mods on youtube and other places, which will at least point you in the right direction.