So Spain, which was fighting the thirty year war and the eighty year war at that moment (and possibly some others I forgot) sends troops to England to fight in some other king's war? Well, that is not going to end well for Spain. Since the troops are probably coming from the Southern Netherlands, my guess is that France and the Netherlands are going to profit most. Probably a Dutch Antwerp and larger Dutch Brabant and Flanders. And of course a larger French Flanders (there probably are still enough Spanish troops in the Southern Netherlands that they aren't completely overrun by France and the Netherlands).
Also bringing in foreign troops, especialy devoted catholics, like the Spanish, is going to be a major propaganda victory for the republicans. I think a large part of the English protestants are going to join them.
Still, unless this was something the Spanish (or the English king) were seriously considering OTL, I doubt it would happen.