So, I was thinking about making a "Grade Mod" in which you could select the minimum grade you want by clicking in the mod (like selecting between DoubleTime/Nightcore), for example: S (It won't be very necessary for Standard, as you could simply use NF), A, B, and C. The game will detect when it's impossible to get X grade, and you will lose.
SPOILER
This is my first post!