The effect would not be retroactive, but I don't think it matters for this case. As I read it, the "that voted in favor of this proposition" clause refers to "Ulm or any Pretenderate or Nation" - that is, 39ers are allowed to attack *anyone* who attacks Ulm or any other 39er. Of course, if the nation you're attacking is ruled by a Wyrm who is himself a 39er, you leave yourself open to attacks by other 39ers. Ermor, however, is not a 39er (yet?) so I'm not on the "open season" list.
I wasn't serious about the grievance bit, just some friendly ribbing...
