Use ballscrews
But, since you have anticipated the problem, you could engineer "split halfnuts" (axial split plane), which you could remove from the machine without diassembly of the screw. As a matter of fact, I have never seen anyone describe this type of antibacklash system, but you could likely rig up a split halfnut with some kind of a push-pull setscrew system that would slide one half of the nut against the other half, to reduce backlash. Because this would not be spring loaded, you would not really be creating an unneccessary wear load on the nut.