Banned for?
Will i get banned for using custom skins? Am i allowed to use a custom skin?
Will i get banned for using custom skins? Am i allowed to use a custom skin?
As long as you dont use it to offend people or just all around use it as an exploit (cheating) it is okay to use Custom skins.
Proof: http://forums.na.leagueoflegends.com/board/showthread.php?p=27906871#27906871
Important to add that certain programs (like MKLoL) which offer custom skins also have other options in them, so that even if you don't use those features, you can still be banned for them.
As the Rioter said in that post, anything like this you do at your own risk.
Given all the recent perma bans for third party programs, I personally wouldn't risk it.
Seems like its super difficult to get a conversation going w/ Riot if you're banned for using external programs