A reskin won't change mechanics or abilities. Will it change the look, animations, possibly do something g like switch fire stacks to ice stacks or something? Sure.

What it won't do is give you anything different. So let's say you got Shiva and reskinned summon 2 with her, you can bet you'll get the same functionality out of the egi that you would have if it was the default garuda.

So take your eye roll and pause for a second, look around d in the back of your head and see if you can't find your brains.