Me also get a warning but i never used it. Only 1 time to try it out its still to years ago...
So i just deinstall LoL and Run CCleaner to clean registery + reinstall LoL and contact the support. So be sure you remove all files -> MK Lol/MK JOGO if you dont wanna receive a ban.
PS: All third party applications which change the oringal clientsettings are not allowed.