Can i take perma ban for custom skins?

While I haven't particularly seen any cases of players being permabanned for custom skins, I will warn that it is possible, as it would count as use of third-party software. Personally, I'd advise against it.

Any changes to the game files can result in a ban once detected, if I remember correctly.

Depending on the software rendering it, there may be hidden elements that allow you to give you gameplay advantage. If Riot deemed that software to be able to alter gameplay (even if you don't use it), they will permaban your account.

Custom skins are currently under "use at your own risk".