I done mine using a common event handler linked to the Connditional Branch... Like skill in away...
Once I equipe the Item I made it so it gave the Char a Skill, like fire fighter, if you activate the skill then I had a conditional branch assign loads of new skills to the Char, change the sprite and all sorts... it even works in battle...
I know it may not be exactly what you want, but it breaks up what your trying to do, makes it much more simple.
If CHar has Fire ring equipied, give skill fire ring Activate... on the skill fire ring add the common event to assign the skills, like Inferno, or summon the God of Hell fire...Etc... once the battle ends or a certain amount of steps are taken turn the skill back off... Make it minus what ever MP you like also...