It all resumes to this line: " Exploits are uses and abuses of game mechanics to obtain an unfair advantage over other players including creating a detrimental play experience." from the Official Servers - Terms of conduct, guidelines and procedures
This means that if you modify things to obtain an unfair advantage ( compared to a non modified version of the game ) then you expose yourself to a ban . Not necessarly the ban will happen , more over if the modification you done goes unoticed but that also means it doesn’t really give an unfair advantage …
From my point of view , except for QoL like removing the intro cutscenes at launch of the game , if you play on an official better not modify any files at all
but that doesn’t mean you can’t play on private servers with mods at the same time , you can easily switch your mods and remove them from the ingame list when you play on officials and put them back when you play on modded ( for example my solo game is full of mods I tested ) but I play on officials online 