Oi, I know this is an ancient topic long lost and forgotten, but the concept I see behind it is interesting, and shockingly similar to what I'm looking for...and it seems it was never resolved.
I am personally trying to make it so that there is a way to alter elemental efficiency via a skill, or state in battle, but when I went to follow this...in rmxp, under the state menu you can only seem to add elemental defenses, rather than take them away. Nor can you cause a state to allow another state to happen specifically. Granted, via ToNs, using chain status can allow one state to lead into another... I still am at a loss as to how to drop an enemies' oh say...fire resistance.
Anyone have any ideas? This is the closest topic I could find relating to this.