If I use a scroll of Polymorph Any Object to permanently turn into a dragon, can I use an Alter Self spell-like ability to turn into an human for a few hours? And when I stop using it, do i return to my dragon form?
Both spells are from the Transformation (Polymorph) school, which says:
You can only be affected by one polymorph spell at a time. If a new polymorph spell is cast on you (or you activate a polymorph effect, such as wild shape), you can decide whether or not to allow it to affect you, taking the place of the old spell.
If you cast Alter Self, the effects from Polymorph Any Object are lost and you cannot turn back into your previous polymorphed form.
Also, Polymorph Any Object does not turn your character into a dragon, it puts a magical effect on your character that changes his form to that of a dragon. What means that if you are a Kitsune, your creature type remains Humanoid, it doesn't change to Dragon nor you actually become a dragon creature.
So, even though the spell duration says Permanent, it is still an on-going spell effect, that can be dispelled at any time, such as when you decide to polymorph into a new form.
Spells with Instataneous duration (such as Cure spells) do cause instant and permanent changes that cannot be reverted or dispelled, which is not the case here.