his behaviour already was somewhat irrational before though.
OTL the duke of alba became commander of the troops in the low countries, a position that was planned to go to don carlos.
so ittl he gets that position, it could cause a lot of changes.
depending if his dislike for his father already existed or not is what is the big question.
assuming it already did, it is very well possible that he will side with the dutch revolutionaries. if he doesn't side with them, then the spanish defeat will only be bigger, since he will lack the military skills that alba has.
one interesting thing could be how much the religiousness of his father played a role in the dislike don carlos had for him.
imagine don carlos siding with the revolutionaries, accepting to be stadtholder and converting to protestantism.
that would not only send shockwaves, but also would influence conversion to protestantism in the south.