It is absolutely possible, Up until the War of Spanish Succession The Crown of Castile and the Crown of Aragon were administered Separately although in the years of Habsburg control Spanish(castilian) became sort of emphasized in government and those who spoke Catalan got pushed out.
When Carlos II died, the country became divided along the Crowns. The people of Castile supported Carlos's will that Phillipe be the next king, The People of Aragon supported the Habsburg Claims.
When the dust settled in 1714 and Spain passed to Philip V, it was then that Spain truly became a De Jure united country. Also Philip then stripped the Crown of Aragon of most of it Autonomy as punishment for their lack of support.
Ive run this scenario in my head a couple of times, Assuming the split fell along the crown lines, it would be logical for Philip to get Castile and the oversea colonies. But the problem is by 1714 the Habsburgs were fresh out of Males to become King of Aragon. And Britain and the rest of her Allies weren't about to let Austria to control Aragon, Most of Italy and southern half of the Netherlands. so ultimately you will need a spare Habsburg male, you will need either a junior branch of the family to be available to be able to step up, Maybe have Ferdinand III's son Charles Joseph not shipped off to the church, he was made the Grand Master of the Teutonic Order at age 13 only to die two years later. He was also Bishop of a few places. Anyway if you can have him live and marry someone who isn't his cousin and have a son or two, you would have a candidate for the Crown of Aragon and possibly avoid the upcoming War of Austrian Succession.