Why not?
Why would they do that? They have never claimed Galicia!! Probably Olivenza and Ceuta, but Galicia?
It was not a question of previous claims, or not. Obviously Oliven
ça and Ceuta would be among the spoils. But it was more a matter of politics. It is a scenary where the Republicans win the civil war, Salazar's portuguese government would face a hostil government in a historical adversary nation (rather a friendly political aligned Franco regime like in our OTL). In this case, and considering that Portugal supports the Spanish Nationalists, the surviving Republican regime would look to Portugal as an enemy, both in terms of international politics as well as idiology. Adding to that the historical Spanish ambition to rule a united Iberia.
To counter this, and considering that Hitler would go after a Republican Spain after the fall of France, I can see Salazar supporting such a move and asking in return the return of oth Olivença and Ceuta and the union of the "protoportuguese" (Portuguese language evolved from the galician idiom) speaking Galicia with Portugal. Other changes would, perhaps, be the a appearence of other indepedent countries under facist/nazi regimes in the Peninsula: The Basque Country, Catalunia, and Canary and Balear islands and maybe, even, Granada in the southern part of the Peninsula. This way Salazar would meet his political goals of mantaining an independent Portugal while weakning Spain to such a degree it would no longer be a huge threat.
Please remember that these are sugestions of a possible ATL, so everything is possible, no? Anyway, I always look forward to your input and coments since you seem to be really well versed in Iberic history and social reality.