Tome of enlightenment;This Hero has 2 additional inventory slots for Magic Attack cards.

Frost token placed on a upgrade slot removes all text etc, treat the card as blank.

So ToE + FR the two magic item slots given by the Tome no longer exist, those items are discarded? (or choice of what you keep?)

Rulebook statements:
REWARD CARDS; When a player accomplishes that Quest, his Guild immediately gets one of the available Reward cards. The card is immediately placed in the inventory of any of that Guild’s Heroes and it can be used nor-mally from then on (the player can discard one of his Upgrade cards to make room for his new Reward card if necessary).
PERMANENT CARDS; Permanent cards are never exhausted, so their ability is always at the disposal of the Hero who has it in his inventory.
UPGRADES; If a Guild has more than 12 Upgrade cards, it will have to discard any excess cards.

I can see a ruling on this go both ways. The items stay in "frost token limbo" and don't fall off a character, or do fall off as you have no item slots to hold them.
(Similar to the life explanation in rulebook, where if your hero has more damage than life without the frost tokened gear,it dies.)