I was hoping for the old 3.5 interpretation, but the errata make it pretty clear:
FAQ/Errata
If I wear a headband of vast intelligence, do I get retroactive skill ranks for my Int increase in addition to the skill ranks associated with the item?
No. The skill associated with the magic item represents the “retroactive” skill ranks you’d get from the item increasing your Intelligence. You don’t get the item’s built-in skill ranks and another set to assign however you want.
[ Source]
https://www.d20pfsrd.com/magic-items/wondrous-items/h-l/headband-of-vast-in telligence