Change texture of an existing mod... but it does not work.

[Gryve]

So this is my first mod and i made a custom character and want to give it a custom item, i noticed that an existing mod of deadpool has the item that i need (his katana) and i want to reskin it to make it look like an Axe.
So i copied all the files and the katana works fine BUT when i changed the texture with the .tex  they have the shape of the katana and the inside of my axe a bit distorted. so my question is, someone of you has a good tutorial on how to make a custom axe with no durability or knows a way to change texture from other mods without problems like that?