TOS lives here.
I don’t have authority to say what is or isn’t a violation, but it doesn’t seem like you would be breaking any rules. There have been monkeypatching threads before (Suggestion: add another set of stones with customisable color - #5 by okonomichiyaki, How to remove the OGS logo from your Chrome browser), though admittedly, these scripts only made cosmetic changes, didn’t do something another user can see, like chatting.