Electronic dampers are different and must be isolated prior to sealing.
There is no problem with adding or changing duct work. The only issue is that the section of new or modified duct will not be sealed. In order to maintain a relatively efficient seal the sheet metal workers (or the homeowner) should tape the new joints (metal tape not duct tape) prior to any drywall being replaced. It would not be cost effective to re-seal the system unless a majority of the ducts were being replaced.