I'd just cut the affected area out, or if it is wide spread, h2o2 sounds like a good idea.
FYI Drying a cactus should only take 1 day. Simply cut into 1/4" slices or thinner, put on cookie sheet(s) and point a fan at it. Flip after 6-10 hours, or whenever top feels dry. Done after 24-32 hours, sometimes less depending on thickness of slices. No heat required.
Even without a fan, cut into 1/4" slices, stand them up and wait 2-3 days......but a fan really helps.
Do be careful, A FEW molds give off waste that IS highly toxic (from experience growing mushrooms, but they are not white, but rather black or yellow molds), so killing the mold does not always = safe for consumption. It is not the mold in these cases that is deadly, but the molds waste. Killing the mold does not destroy these toxins.
Though, I'm not sure any toxic molecules would a) survive the B/A extraction b) be carried over to the NS solvent layer and end up in the final product....so you are probably 100% fine using the molded over cactus...