A Question about the Winter Map

They don't currently pursue punishment for custom skin modifications (granted they aren't providing an unfair advantage), but make absolute sure that whatever you are using to do it does not provide any other feature than that. If the application does anything that violates the Terms of Use (like special timers or scripts) then the entire app is off limits and you'll be banned for it whether you use that particular feature or not.

Here are some resources for Riot's stance on 3rd party apps and guidelines for determining what's typically ok and what isn't. Keep in mind that any 3rd party app use is "use at your own risk", so if you are unsure whether it's ok or not, ask and/or don't do it;

http://boards.na.leagueoflegends.com/en/c/miscellaneous/5kx4F7VE-reminder-third-party-applications

http://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/5dmkJinG-3rd-party-applicationsmodifications-whats-allowed-and-what-isnt