No way, but it's true...

I thought it was just specified that getting this event buff required garrison duty, and wondered if using operators there would prevent them from being used in the main stages. Turns out it's true... I don't have many operators leveled up as it is, so if I use them all for garrison duty, I won't be able to play the main stages... ㅠㅠ I guess I'll just get a small amount of buffs and try to figure out how to best utilize my good operators in the main stages...