Is a custom screen resolution allowed?

https://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/5dmkJinG-3rd-party-applicationsmodifications-whats-allowed-and-what-isnt

Here, they claim that changing the game to a custom resolution in the game.cfg is not allowed because it could potentially be used to give someone an advantage.

However, the game only supports one 16:10 resolution in my settings. I need to optimize to get better FPS and one of the ways I can do that is by playing at a lower resolution that is still 16:10 ratio. But I would need to input that resolution manually into the game.cfg to do it.

Is that allowed, since it would impart no advantage to me to be playing at 1280x800? I might even try 640x400 but I don't know if the game is capable of going that low.