the process is called sku conversion.
A lot of Gamestops actually have sealed copies of games like Steel Diver 3DS brand new sealed but they sell it as pre-owned.
I used to try and keep up with it, but it doesn't happen very often. once a month to once a quarter and it's never good games. Last few times I asked about it, the employees acted like I have no clue what they are talking about. I even tried to grab one of the Wii U kiosks when they swapped for Switch kiosks, but every store either trashed the kiosk beyond use, got swiped by preferred customers/employees, or some lucky fool managed to snatch one. But when I asked I'd get the response of either "Oh, the Nintendo rep has to come and collect it" or "Oh, we destroyed it so it would fit into the dumpster."
I think I got Heavy Rain Director's Cut sealed for the pre-owned price 5 or so years ago. I got Master of Illusion sealed for $0.89 a few years back with the playing cards and stuff. Last Story launch edition for like $30 or 40 sealed.
Most of the time they don't unseal the games, they just keep them in the drawers.