With the MFR rail sections, you don’t have to completely remove the screws from the backers.
Loosen the screws until the rail can slide back and forth in the slot. Slide it all the way to one end of the slot. The lip of the backing plate should drop out of the rail slot. Then you can slide the rail section in the opposite direction until the other backer comes out of the slot. It sounds way more confusing than it is. Installation is the reverse of the above process.