I noticed there's a couple of bans for people using modified skins.
Does the client know it's using modified content or does the server it's being reported to figure it out?
If it's the client I suggest that the client could delete the offending skins or move them to some other folder to be nice and then when they connect to a map the in game downloader should grab the content from the server. Maybe apply the checksum mechanism that notices when your map file isn't the same as the server and auto re-downloads.