I have two 'installations' (well, just copied the folder). One is a barebone fresh-off-the-cd installation with nothing tweaked other than my resolution and custom maps. The other one is chock full of skins/model/sprite replacements, binds, etc.
For all of you who play in leagues but still want custom models, I suggest doing the above.
As for custom models in MCC, I think we should be required to use the original ones. Unless we're required to sumbit screenshots/take demos/etc.
Then again, MCC is only for respectable clans in the community. I guess players who can't be trusted with such things shouldn't be playing in it in the first place.