Demo plans need room tags so a contractor knows what room to demo stuff in. Room tags can't tag a room in a demo plan because the current phase is set to new construction.
How can you get room tags to identify the existing rooms? Overlay views on a sheet.
Create a new view assigned to the Existing Phase.
Using Visibility/Graphics turn off all Model categories except Rooms.
Now your view only shows rooms and room tags.
On the sheet that displays the demolition work, overlay this special room/room tag only view above the demolition view. A little bit of extra work but you get automatic display of the correct room information without resorting to "dumb" text and introducing possible errors.
As an aside, I believe that rooms should behave more like other model elements and have a "Phase Created" and "Phase Demolished" parameter. This way an unaffected room can persist across phases. Rooms whose boundaries are demolished should also be demolished and require the creation of a new room. In this way a demolished room would still be visible and New rooms would not according to the view's Phase Filter setting. I'm sure there may be some programmatic conundrums that this might introduce but overall this is the sort of manner in which Rooms should behave...in my opinion.