Removing Existing Light Fixtures from Schedule Quantity Counts
Quantity counts in schedules include all instances of each light fixture in the project. There is no way to filter it to exclude individual light fixtures.
If you want to exclude existing light fixtures from the counts, you must create a separate schedule entry for the existing light fixtures. Add something to differentiate the entry from others, such as an "E" following the name.
In the Light Fixture Project Schedule, uncheck the ☐ Include in Schedule box. This will remove the light fixture from the schedule inserted on the drawing.