While there are many different brands of shower doors I am not aware of any I have installed where the guides can be removed without taking up the bottom strip.
This isn't impossible. You lift off both doors and the header. Unscrew the side jams and remove the bottom rail that is caulked onto the tub. However I've not heard of anyplace where you can get just the guides and the bottom rail would probably have to be ordered from the manufacturer. Most doors do not have the manufacturers name on them.