In this case, it ought to work exactly the opposite of how you think: a Congressional resolution is supposed to be the only thing that gives Trump authority to engage in war to begin with, so the only thing vetoing one ought to be able to accomplish is to remove that authority. There isn’t supposed to be such a thing as as resolution disapproving of the President’s unconstitutional unilateral action; if anything, what Congress just did should be treated like revoking its prior approval and thus not be vetoable.