How is this is even an issue, except for the aforementioned "putting present political perspectives into past problems"? Portugal wouldn't be "flipping" or "switching sides." If Spain doesn't exist, then there is no Spain for Portugal to say "we don't want to be called Spaniards!" They could form Spain, and tell those stinkin' Castilians & Aragonese to shove off - they can't be the Spaniards! In this scenario - there is no "Spain" for Portugal to dislike - they would be the Spain.
I'm sure this is near and dear to the native Portuguese, but look at it from the standpoint of THERE IS NO SPAIN YET.
I'm sure this is near and dear to the native Portuguese, but look at it from the standpoint of THERE IS NO SPAIN YET.