I had the same problem with the equipment for Crono. There's a lingering 3rd byte that can mess with things.
Also, the hero's MP can go up above 100, but it doesn't show correctly in battle or outside the menu itself.
Edit: Just a note, the helmet/accessory modification codes are rather weird. You can't alter their values at all, the game will freak out ._.
Edit 2: They are in different locations:
2207296A 000000VV - Helmet
2207296B 000000VV - Helmet 2? (Strange 2nd part for helmet)
2207296C 000000VV - Accessory