I'd like to take this idea even further: if you had a state that swapped parameters. So for example you add a state that would temporarily switch a powerful tank monster's def with their atk, which effectively makes them vulnerable to actual attacks (but also makes them ridiculously powerful)
Now, what happens if you have one equip that swaps atk with def, and another equip that swaps def with atk?
Do they cancel out?
I like this better actually. It would be easy to apply it to armor with YEP Passive States. It also introduces interesting buff/debuff mechanics, which I shall call "rebuffs".
In terms of cancelling, I think yes. If you think of it as an Order of Operations type thing, if you had two equips that both swapped ATK and DEF, the "first one" in the list would make ATK => DEF(atk) and DEF => ATK(def), then the 2nd one swaps again, making DEF(atk) => ATK and ATK(def)=> DEF again.
Even MORE interestingly, what if you had 2 equips, one switching ATK and DEF, another switching DEF and MDF? I think this would definitely need some type of order, probably in order of the listed equipment, such as in the Equipment window. So if you had a Helmet (3rd listed Equipment) that swapped ATK and DEF, and an Accessory (5th listed Equipment) that swapped DEF with MDF, first ATK would become DEF(atk) and DEF would become ATK(def). THEN the new DEF gets swapped with the MDF, making DEF becoming MDF(def) and MDF becoming ATK(def){mdf}. Ultimately, in this scenario, ATK would have the value of your original DEF, DEF would have your original MDF, and MDF would have your original ATK...
Man, this turns out to be much more indepth than I originally thought...