Hello Firancil,
Lomar, an Associate Producer for Riot, talked about Custom Skins in this post. In short, he states that they don't ban for modifying things that are not harmful to the other League of Legends players. But you are using the custom modifications at your own risk.
Here is the full text from that post:
I find it a little curious how the thread starts out with "modification is against the EULA (and the ToS), so you might get banned!" and then it slowly creeps into "a lot of people have been banned". All without substantive support.
There's some misinformation here, so allow me, as the dude responsible for that document and the policies behind it, to clear this up a little.
There is a no-modification clause. It was there on the first day LoL launched. The no-modification clause hasn't been modified (heh) since then.
This is something pretty standard you'll see in EULA/ToS documents for most software. The objective is to give a software maker more angles to pursue hackers or other parties that are changing software in a way that harms the original maker. Copyright law (e.g. the DMCA) gives you this same exact ability, but sticking it into a contract like a EULA/ToS just gives you an additional angle of approach. But I'd go take a look at the legal documents for other commercial software you own - my guess is you're not going to find many lacking a no-mod clause.
Now that said, a legal document really exists to just create a set of potential rights. No company enforces every provision of their EULA/ToS, and they enforce to varying degrees. Different violations have different implications to the business, and there are varying costs to enforcing. You don't just push a button. Some enforcements, like takedowns of phishing sites, can take months and cost thousands. So what that means is any company, from MSFT to Google on down, is selective.
In our case, we've made a decision that custom skins/splashes aren't necessarily hurting the business. Our business is in making our players happy - the ability to custom stuff is likely what keeps certain people interested in our game, and acts as a force multiplier for other people. From that perspective, banning people is incredibly stupid. We're forcing people out of our game, and lessening the experience of other players, for no real clear benefit.
That said, it's important that we reserve our rights to defend the IP here. There may be certain custom skins (Nazi Teemo!) that we may have a legitimate problem with. And there are other modifications (Zoom hack!) that are a certifiable balance issue and need to be prevented. Custom creation will always be at your own risk - updates may break functionality, etc. But we also aren't going to just toss out arbitrary bans. It's not in our players' interests, and so it's definitely not in ours.
TLDR: No-modification clauses are standard in software EULA/ToS documents. LoL has always had one. Custom-modding is always at your own risk, but we generally don't ban for anything unless it's clearly harmful to LoL or our players. The vast majority of custom splashes/skins will NOT fall into this bucket.
I'm not aware of any, but if you believe you ARE a legitimate case of being banned solely for modification of skins/splash art, send in a support ticket with specifics and reference me in the ticket. I can promise one of two things: a) it will be corrected; or b) you'll get a good explanation why it won't be.
If you are curious, the no-modification clause is in the EULA -- Section III, Subsection C:
#III. ADDITIONAL LICENSE LIMITATIONS
...
You agree that you will not, under any circumstances:
...
C. Modify or cause to be modified any files that are part of the Software in any way not expressly authorized by Riot Games;
Hope that helps!
