Here I can think in a worse political problem, since we talk about guerrillas. There were thousands of exiled republican spaniards fighting alongside the FFI, often with their own command and direction. ....
....So, how are they going to react to the (to be honest, very very unlikely) fact of Franco being now on the side of the Allies? How is Franco going to deal with the fact that his archenemies, the "anti-Spain" are part of the allied armies? t...)
A legitimate question. My answer is it will make French politics of those same years look like a walk in the park. Franco will not be able to control every faction and the hard core anti communist and pro facists will organize a resistance to both the Allies and any returning exiles. Franco will best prevent any exiles from returning & those already serving with the Allies need to be kept in segregated formations, much like some of the more rabid French factions had to be kept apart. The Germans & Italians will sponsor the return of the Division Azul (if it exists in this ATL) to fight the Allies. Since the Germans established agents in Algeria when the Allies invaded there OTL its likely they will do the same in Spain. Its closer, so parachute delivery is practical, as well as submarine and infiltration across the Pyrnees. No doubt profacists in Spain would attempt the Pyrenees in the winter to join with whatever Axis sponsored group exist.
Worst case for the Allies is a coup eliminate Franco & the Spanish army disintegrates into several factions struggling for power. In that case both the Andalusians & Basque may attempt to negotiate something with the Allied commanders in their territory.
Best case for the Allies is of course a surviving Republican government. There may still be attempts at coups, and there may be tens of thousands of pro facist Spaniards on Axis turf, and a anti Allied resistance inside Spain. Still this alternate favors the Allies in a number of ways.
in late 1944 about 10.000 spanish partisans tried to invade the Aran Valey
For those who don't know this story, it did not stop there. Efforts by Republican exiles to infiltrate into Spain and start a uprising went on after 1945. While by 1950 the movement was a dead letter, exiles continued attempts to revive it up to Francos death in the 1970s. The Basque independence movement was a independent faction of this effort.