There will be one very good reason for changing the state of registration of the Koda 707 - since aircraft registered in Equatorial Guinea (3C-) are no longer permitted to fly in UK airspace, it would need to change it's tail # or be scrapped. She's worth next to nothing as scrap, but a few revenue flights could well generate enough revenue to pay for the purchase of the airframe.
If the rules let you do it, then people will do it!