Can i use custom skins in game?

Pretty sure that would be classified as third party software that would interfere with gameplay which would in turn permaban you.

3rd Party Applications/Modifications - What's allowed, and what isn't Wuks (NA) submitted 2 months ago in Player Behavior & Moderation

Custom Models & Artwork (Skinning) - Allowed (for now)

Riot, not too long ago, announced their stance on using custom skins and models. Essentially, these modifications can cause issues on your end (Bug Splat/Game Crashes), and generally have the potential to impact gameplay. Riot will be keeping an eye on custom skins, and if the policy changes, they'll likely announce and warn before taking action. I'll do my best to keep this updated; if you notice Riot changing their stance, feel free to comment below! NOTE THAT THIS DOES NOT MEAN MKLOL/MKJOGO IS ALLOWED. See the MKLoL/MKJOGO section below for more information.