This is somewhat difficult to explain. Basically, I want to dynamically assign textures to a few items. I have it all done, however I do not know how to do this one bit:

 

Let me show you an image first, then I will explain.

 

Let's say I have texture A, and I want to replace the green part with texture C. What I want to happen, is it to replace the green part, and replace that part with the exact spot from texture c. Same thing for textures B and C. How would I go about doing this? (Note: these are simply demonstrative images, not the actual textures I wish to use. Also, sorry if this is an awful explanation.)

 

Also, while I know this is possible in 1.7, is this even a thing that you can do in 1.8? Haven't messed with the model files much, but wouldn't you need a model file for each item? That would mean it couldn't be dynamic...

 

To clarify, I want to do this on 1.7.10, but I am curious about the possibility of doing this on 1.8.8 as well.

Above and just maybe:

 

For 1.7.10: IItemRenderer and GL (in your case kinda lot of it).

1.8+: ISmartItemModel (not sure about "I" at beginning) or any other interface + manipulating model registry.

 

In both cases you could also utilize layers (but those can be only 5 last time I checked).

Here's a custom TextureAtlasSprite that does pretty much what you're looking for.  It takes in two textures and combines them.  You'll have to modify it to combine them in the way you want, however.

 

http://www.minecraftforge.net/forum/index.php/topic,35760.0.html