I currently on leave from ExpressJet. When I went through initial in 2016, we toured the maintenance area. I remember someone saying that if a plane goes back to the leaser, then everything has to be returned to the same condition as when it was first leased. Any new software in the computers have to be returned to the original database, any engines that have been changed out have to have the original engines reinstall by serial number, so I'm not sure if that is the same if transferred to another carrier.