If another player gains control of Gift Shop and then visits it, they won't be able to choose a mode you chose while you controlled it
Your reanimation stuff that would normally only do something with your own graveyard will now potentially target anything, such as Immortal Servitude or Obzedat's Aid
That said, you should definitely put them in a sleeve whenever you find one
Cecil, Dark Knight becomes Cecil, Redeemed Paladin, for instance, while Garland, Knight of Cordelia becomes Chaos, the Endless, and Emet-Selch, Unsundered becomes Hades, Sorcerer of Eld
He was adamant that he wanted an exalted deck, not a voltron deck focused solely on buffing a commander with double strike