So if they are wifi safe, there should be no reason they couldn't be used in a competitive environment?

That helps a lot, thanks so much guys!

If the bones aren't edited in any way it should be fine, hitboxes are attached to bones and I'm pretty sure hurtboxes are too, so missing objects shouldn't affect gameplay. Size modded things and the like will affect gameplay of course.

Really if you put it on your SD and it doesn't freeze it should be fine.

And the question here is how do I know if bones have been added or not? Should it say somewhere on the description?

This is actually sort of a double question. It's been a while since I put alternate costumes from here into SSBB, but now that I've been playing PM so much lately I want to mess around with it again.
I've seen some people say that certain costumes don't work with PM. Do the costumes have to be specifically made for PM or should every one that works for SSBB also work for PM?
My other question is how do I know if the character has been tweaked in any way (specifically hitboxes and hurtboxes)? In other words I still want it to be a competitive build. Even though this is just for me and I wouldn't use this build for a tournament or anything, I would still practice with it and I don't want any kind of change that is different to how the character originally is. For instance, maybe a scarf hanging off a certain character wouldn't bother me, because obviously there wouldn't be a hitbox for it. But if there was a striker Peach costume, it would mess people up because the hitboxes would look different since she wouldn't be wearing a skirt.
Do import model texture, texture, import, and the rest give all the info I need? If so what do they stand for?

For example, I'd love to use the Lucina and Rosalina costumes from LST or Toon Link's Tunics from ShinF and many more, but I don't know if they could be used with a competitive build?

I've asked this in another forum, but felt like this would be the best place to ask. Thanks for all the help!

I want to add the mango Pit alternate color scheme and the character select portrait that comes with it, but with PM 3.0 it won't have the alt. costume bar with the csportrait. Is there any way we can add that bar to the csp with a simple render of it? (I would be using paint, lol)