Go into build
Find the hat you wanna retexture
Click its mesh
Copy it's link to the texture
Make it item.aspx,like a normal hat
Add +1 to the number(EX:54645 becomes 54646)
Save it
Edit it
Have fun!
Put the texture in the textureId of the hat you wanna retexture.
http://www.roblox.com/Item.aspx?ID=6547852
BTW,never mind the step to add one.I was wrong about that :P
THOUGHT FORTRESS TEXTURE ABOVE