IMHO one of the best and safest ways to 'swap' sandbeds is to set up a remote sandbed, ideally in a fuge, that is large enough to carry your whole system.
Example: I have fine sand, and find it a PITA with a high flow. It walks. So I am replacing it with medium-coarse aragonite. Note my relative sizes: I have a 54g tank with a 20g fuge. Both had a 3-4" sandbed. I have now siphoned out most of the fine sand from the display, but the system is running optimally, because the fuge sandbed, which is very rich and pampered, along with its live rock (20 lbs) is carrying the whole system quite handsomely. Not a hiccup, not a blip.
Raw sand usually arrives with some phosphate bonded into it: so when my sand order FINALLY gets to my lfs, I wil begin by adding a couple of cups of *washed* sand via fat pvc pipe straight to the bottom of my display tank. I will get some more hermits and snails to poo the resulting green algae straight into the water column, where it will arrive at my fuge and the phosphate-loving algae down there will suck it up.
No cycle, no blip, just a bit of algae growth which will get handled fairly fast. Bacteria from the fuge will arrive and colonize the new sand; and every few days, another pound of sand goes in. I'll judge by the behavior of the tank how fast to procede.