Going out from Swampy to Oz I found that there was an immigration office upstairs where you could just attend before the flight and get a multiple entry permit converted from a single entry. 3800 baht I think. Done within minutes as they don't have much going on in that section. Not sure if the current situation has changed it around. Loy Toy put me onto so you can thankhim if it's still available.

This was preparatory to going out of LOS but I think it could still work coming in provided it's office hours I suppose.