whenever respraying a popcorn ceiling I always paint the ceiling prior to the spray. If you dont you stand the chance of the bleeding discoloration.
as long as the amount you scrape off is consistent over your entire ceiling, youre safe to respray
i spray it with water and scrap to get it pretty smooth, basically the best you can.
prime the ceiling.
then spray the popcorn.
wait a min. of 24hours before painting.
48-36hrs before painting would be alot better.