Reforming after a 14 day suspension is a dead end

Riot doesn't, to my knowledge, exclusively use in-character behavior to determine account sharing. They have MANY methods of detection designed to prevent false positives.

Improving your behavior will not get you banned. Not improving it will.

You don't have to be nice to people to keep from being banned. You just have to not be toxic to them. It may sound a bit grade-school trite, but the old rule of "If you don't have something nice to say to someone, don't say anything at all" is pretty helpful here. If you're genuinely worried about being too harsh with teammates or opponents, then just do your best not to talk to them.

Mute them if you have to at the beginning of the matches, or at the first indication that they might be saying or doing something that irritates you. It will help you be less tempted to snap at them. Some people unbind their enter key, others hide the chat window. There's a lot of different things that can be done to help you control how you interact with them.

What many people do not realize is that being toxic is a habit. It's a pattern of behavior that people fall into, and they let it snowball until they no longer remember how to not act in that manner on the internet. But like any other habit, it can be changed, or even broken, in time. A general estimate is about a month's time of consistently not indulging in a habit to begin to break it and recondition yourself to act differently.

It's hard to just quit anything cold-turkey, so it may take you a while to work up to being able to fully break those habits. But if you start small, you can do it. Start with just telling yourself that you're going to play a match without snapping at your teammates. One match. It's only 20-30 minutes. You can do that. Mute them, move the chat box down some, don't read chat, whatever you think will help you the most, do it. Your goal is just to not type anything toxic, either at them for their mistakes, or in response to something they say (which is where the muting helps). And once you've finished that match, exit the lobby and you've made the first step.

We won't ask you to do anything hard, or try to make yourself into someone you aren't. No one will try to force you to type "GG WP ALL!" if you didn't think it was a good match. All Riot asks of you is that you don't type "BG KYS %%%%%%%" and rage at your team if you think it was a bad match.

Step two isn't any harder than step one. It's just doing it for two matches. And then three, four, five, until you can play one whole day without snapping at your teammates, or flaming them back if they say something to you. Before you know it, you'll be up to a week of not snapping at anyone. Then two weeks, three weeks, then a whole month. One entire month where you've literally done nothing more difficult than type /mute all, or pressed a button next to a person's name in a match. You can do that. It takes self-control to keep from telling your teammates when you think they are playing poorly, but you have that. It takes maturity to know that your account is worth more than getting the last word in with some punk kid on the internet, but you have that too. You have all the tools you need. You simply need to use them.

You're an idiot. Plain and simple.