You gave an example of a ruling that adds upon or alters the function of a magical artifact on the DM's own accord due to a RAW player action. You do realize that half of the threads discussing magical tricks, strategies, actions, spell combinations, magic item uses and so forth would be completely obsolete when it comes to the DM arbitrarily making a decision which adds to game mechanics in order to "balance" it, right? You should be asking like a hundred guys on this forum the same question.
I would not say it "has no sensible application". A DM could just as well decide to let it be done regularly, exactly as you would expect ( minion uses deck, gets effects of deck, nothing else of any special import happens ) and move on, either not minding the supposed "balance infraction" or allowing the player to be rewarded for exercising his brain. Some DM's do it that way.