Make an auto-run event to to turn a switch on...for example "Club On" <-Switch Name
Don't turn the switch off at anytime while using the Club or you'll keep the class regardless.
Make a Common Event and call it "Club On" (Or Whatever). Trigger=Parallel, Condition Switch= "Club On"
What to put in...
@>Conditional Branch([Character]=[Weapon] Equipped)
@>Change Actor Class: [Character], [Class]
@>Change Actor Class: [Character], [Normal Class]
: Branch End
Now every time you equip the club you'll change class. No need to call the common event.
Class change won't occur until you exit the menu screen.