Man I was totally overlooking the fact that each of the 2d model's bone has it's own offset! After seeing this I could finally understand what you were trying to explain about applying the changes bone by bone. Sorry about that!
But, if I'm not mistaken, and as you say, the only way to make a 2D model look like this is just darkening the texture.
I don't know if that is the only way to do it, but it is the only way I can do it so far. And that was what lead me to try and edit the 2d model's normals.
The block model and the 2d model that I'm using shares the same texture, are positioned side-by-side and haven't had their rotations edited at all. In inspite of that, the 2d model didn't seem to be affected in-game by lighting the same way the block model was, and this was really annoying me. Both of them were supposed to have that darker color you see on the block model by the picture but the 2d model just wouldn't cooperate.
I should stop talking now lol
Well, thank you once again for clarifying everything. I owe you that, Mewtwo.
Edit:
Also, unless I'm mistaken, there's no use in rotating the normal in the 2D model, cause the only place you will see the change will be in brawlbox. If things are the way I guess for that model, it will always look the same in-game.
Unfortunately you are not mistaken. The 2d looks fine in Brawlbox but won't change in-game.