I'm pretty sure that, by RAW, the Polymorph Any Object spell would function like the Alter Self spell when talking about specific physical aspect. But would it be balanced to allow Human A to polymorph into Human A2 instead of Human X with Polymorph Any Object?
By default, polymorph spells cannot be used to mimic the appearance of a specific creature, as per the rules for transmutation (polymorph) spells:
Unless otherwise noted, polymorph spells cannot be used to change into specific individuals. Although many of the fine details can be controlled, your appearance is always that of a generic member of that creature’s type.
The spell polymorph any object can act as greater polymorph, which in turn can act as alter self. These are all transmutation (polymorph) spells. None of them specify that the target can be made to look like a specific creature, so by RAW, it is not allowed.
Magically impersonating a specific creature would typically require (1) a transmutation that specifically mentions looking like a specific individual, or (2) an illusion like disguise self. And even with magic, attempting to pass as a specific person may require an opposed Disguise skill check versus an observerer's Perception check.
Allowing any polymorph spell to achieve this may be unbalanced, because it is situationally very powerful, and would be providing another spell's benefit for free.