What are the rules for power upgrades in ML? (Not that the writers will remember after three episodes, but I'm curious)

Based off how Ladybug starts making Anti-Akuma charms by the power of just "I Do What I Want", and Shadowmoth overcoming those same charms immediately through the "Anything You Can Do I Can Do Better", I just made a sort of vague rule that if the holder is ever desperate enough, and focused enough, a power could possibly manifest to fulfill that desperation.

I imagine there'd be some blocks, like you can't manifest a power that will completely replace another kwami's power, and if you use the Miraculous for evil, it'll take more than just desperation to make a new power manifest and for evil holders it may only manifest one time. But these caveats probably won't come up since I only have a few episodes left to write.