In every single navigation request, you can specify which behavior tree you'd like to use, so you can easily change behavior every single navigation request if you like. If you'd like to change mid-action, you can always preempt the currently running navigation request with a new one using a different behavior tree (but I assume you mean changing behaviors between navigation requests, not in the middle of a current executing one).
By the way, we support Nav Through Poses & Nav To Pose as 2 separate actions that can be called by default with Nav2, you don't need to relaunch anything. You can just call the action you like (but that's specific to the 2 "styles" of navigation for Nav to Pose and Nav Through Poses). You can't call them both at the same time since they're mutually exclusive, but you can call them sequentially with or without specifying specific BT files for use to your heart's desire.
