I think it would be fairly simple and not very taxing at all. This is how I would do it with a quest script.
scn yourscriptnameref dudebegin gamemodeset dude to getfirstref 69 1while dude if dude.getitemcount yourtoken == 0 ;modify dude's health dude.additem yourtoken endif set dude to getnextrefloopend
In this script I had the NPCs keep the token because it seemed like a good way to make sure their health was adjusted only once.
Alternatively, you could script the token to modify the dude's health instead of putting the adjustment in the quest script.