So, your Feature Request is for KoLmafia to add a new modifier category: StatDay, to put three things into it: StatDay:Muscle, StatDay:Mysticality, and StatDay:Moxie, and apply the appropriate modifier on the appropriate days, if and only if you are out of Ronin/Hardcore?
I wasn't sure if it was a bug for there to be a modifier that wasn't considered as a modifier. I also don't know if it's calculated into "Exp:", though it seems that "Exp:" doesn't consider the effect of +stat%.
Revision 9340 accounts for Muscle Day, Mysticality Day, and Moxie Day for characters out of ronin/hardcore. As expected, the affected modifiers are Muscle Experience Percent, Mysticality Experience Percent, and Moxie Experience Percent, respectively.