I mean, I really enjoy playing as lemongrab from adventure time as yasuo, fighting bill cosby blitz crank and an anime blue haired sci fi girl dunking people as darius, while the fizz is just a fish holding dank weed, and he can make snoop dog erupt from the ground, meanwhile hank hill is blowing up propane as gang plank.
While technically any modification to the game is against the rules and a bannable offense, Riot doesn't currently pursue punishment for custom skins (that don't provide a gameplay advantage). However, all 3rd party programs are "use at your own risk", so if there is an illegal feature alongside it or it has a virus that causes your account to be compromised you are entirely responsible for it. If in doubt, don't do it.
Check out these posts for more information; http://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/5dmkJinG-3rd-party-applicationsmodifications-whats-allowed-and-what-isnt
http://boards.na.leagueoflegends.com/en/c/miscellaneous/5kx4F7VE-reminder-third-party-applications
I used custom skins for a long while. Riot won't care as long as it doesn't affect gameplay in a way that gives you an advantage. Also be careful with which software you choose. Some third-party applications may be notorious for cheating even if you are only using it for cosmetic purposes.
