JennB:
To have a demo plan that shows existing walls with solid lines and dashed lines where the new openings will be, set the Renovation Filter Options for Demolition Plan to:
Existing Elements: Show
Elements to be Demolished: Override
New Elements: Hide
In the Renovation Override Styles > Override Styles for Elements to be Demolished: check Line Type and set to Dashed.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David