[1.7.2] How to make players with a name in a list have a custom skin?

[Miclebrick]

So, I want it to have something where there is a list of names that have a skin that isn't from minecraft.net, but from inside mod files or somewhere else. So, let's say I had a list containing this:

Bob

Ronald

And let's say from minecraft.net Bob has no skin so he's steve and Ronald is some random dude with Ronald Weasly as a skin. Inside the mod, I have Ronald.png and Bob.png. It changes their skin to that. Is it possible to make this? Because I don't see anything like this. (Yes, I have tried google. Nothing that aided me came up.)

[Miclebrick]

bump

[Miclebrick]

I don't understand how to make a coremod. The tutorials I find are all outdated.

[Miclebrick]

I know Java. I just can't find a tutorial on making a coremod that actually works.

[Miclebrick]

Kay, thank you.