Essentially, you can no longer wipe out your default skins and such. However, you can easily use custom mod packs via menu for the game. Whether third party, or you do it from a legit screen, not a terrible problem.
HOWEVER
I think servers should have the ability to force upon users to use their designated mod packs. I'm talking about skins.
If the server wants to run pure defaults (Hint: Skill needed), then hell, they can force people to use the default skins.
If a server wants to run Komrade krap, they can do that too.
It would work just like maps, except the specific mod packs would be loaded onto a folder with the mod pack name for universal use.