The card says that you can select French-controlled duchies in Spain and roll to reflag them to Spanish (with 50/50 probability). Does that apply to fortresses as well? Doesn't seem right that guerrillas could take a fortress so easily but the wording on the card doesn't seem to exclude fortresses.
Dave - thanks for the quick reply. That does seem like the way it should be. I did check the forum threads before I posted but didn't think to look in the files section. That list will be helpful in future games!