1. Can Union of Arras change political control of Brussels from Protestant to Spanish if there are Protestant units there? The card FAQ of the scenario book says no, the card FAQ of the card manifest says yes. If it can, can Spain then immediately build 4 Walloons in Brussels?Can you link to the file or site where the part in bold can be found? Yes, Brussels could change political control if Protestant units are there--provided that Spain and the Protestants are not at war. Any Protestant units would be displaced from Brussels according to the procedure in 12.5 on page 17. I see no reason why Spain could not add the 4 Walloons to Brussels once it's Spanish-controlled.
2. Of less importance, can Spain spend two Union of Arras flips to change political control and change religion in the same space?No. Either political control or religious influence in each of 5 spaces. Gouvernante de France works the same way--see the question and Ed's response on CSW.
EDIT: corrected a goof