I have seen an instance where a player requested a chat restriction from Riot Support, but it came with all the disadvantages; stripped Honor being the foremost.
If I may say, though, I have a hard time understanding how such an action could be necessary. Do you really lack the ability to hold yourself back, and need to have a punishment status applied to your account just to avoid negative communications?
I don't intend to insult, of course, I'm genuinely curious.
Another question I'm inclined to ask; have you tried any alternative solutions to venting negativity outside of chat - breathing exercizes, stress relief (pillow-punching, stress ball-squeezing, fidget spinning), etc.?