I can't really help since I have only repotted my bulbos once officially (when I got them) and don't grow Bulbo. Medusa, but I can say that my plan is to eventually try to pull up as much of the old sphag as I can without damaging the roots and replace it (mine are also in baskets, growing in bark with a thick layer of sphag on top).
I can also say, if it helps, that I dropped one of my bulbos several times and basically had to shove it back in the pot, and it's grown consistently and never showed any signs that this disturbed it, so I think they aren't as fussy as people fear they are