If these linear guides are THK's HSR type it is OK to remove a block from the rail without using a dummy to park it on. I resently inspected and re-sealed 8 HSR 35 blocks from my X- and Y axis. You just slide it gently off the rail. Do not remove the end casings!! If you need to take the balls out to clean the whole thing, take one circulation of balls at a time. If the worst happen and you mix the balls between the 4 circulations, it is not a big deal. Their diameters are usually within 0,5 micron in difference within the same block. Blocks delivered on the same rail will usually have ball diameters of similar diameter ranges. But don't bet on it, never work with several blocks at a time. Between blocks from different rails you may find ball diameter differences up to 2-3 microns. (1 micron is 1/1000 mm). If you want to dismantle blocks comletely for inspection and re-sealing, send me a PM, and I will send more info and pictures.