Can I "hide" a Vesuvan Shapeshifter?
As per the rules reference in the answer you linked (i'll change emphasis to make this clear) :


  707.6. If you control multiple face-down spells or face-down permanents, you must ensure at all times that your face-down spells and permanents can be easily differentiated from each other. This includes, but is not limited to, knowing the order spells were cast, the order that face-down permanents entered the battlefield, which creature attacked last turn, and any other differences between face-down spells or permanents. Common methods for distinguishing between face-down objects include using counters or dice to mark the different objects, or clearly placing those objects in order on the table.


If the opponent doesn't remember that the third face-down creature was the one revealed as the shapeshifter, that's not on you. However, you must be honest about a question such as "Which is the third face-down creature you cast this game?"

CR 707.6 also seems to make explicit that you must answer such questions as "which creature attacked last turn" or the order they entered the battlefield.


  But that can get a bit tricky, as I may move them around in the course of the game, perhaps rearranging for attacking and blocking or anything else.


If you're not using counters or dice to mark the face-down creatures, you must at least keep them always in the same order after combat manipulation, obviously, whether it's "tricky" or not to do so… in a tournament setting you could get in trouble if you don't.

I think, in the spirit of CR707.6, which says "this includes, but is not limited to…" if you're asked "which creature did you turn face down last turn?" – you should answer truthfully. I know this is basically the same as saying "which creature is the Shapeshifter?" but you made the information public.

I'm not sure how this situation is handled in a tournament, but once a creature has been turned face down, as your opponent I would immediately request some sort of die or counter be placed on it so I can keep track of which one is the Shapeshifter.