Yes, Cut the cactus back to good looking flesh with a clean knife. . Brush the fresh flesh with cinnamon(anti fungicide). Let it callus over for a few days and then plant in a gritty mix . DO NOT WATER. Only mist. till it makes roots.

I had a healthy Gymnocalycium piltziorum. I thought I had it in a soil mix that would drain well enough so I could leave the plant outside during the Spring rain showers. Nope. The roots and main body of the cactus rotted. I was left with a bit of healthy looking top layer of the plant. I doubt I can save the little part left but I'm trying to. Meanwhile I want to get another Gymnocalycium piltziorum. For the next try I should use a different soil mix. I read this cactus natively grows under shrubs. What plants are found with this cactus? Maybe I should try planting another plant in the pot with the cactus. Any ideas for plants that can go without water like a cactus and soak up water when it is there? Maybe something with a fibrous root system would work. I'm not sure which microbe rotted the cactus but are there any plants that produce antimicrobials around their roots that might help? Seems to be a lot of antimicrobial extracts from plant roots.

"You can't propagate a cutting of anything without water." This is not true. In fact, most succulent cuttings will melt if they are treated "as if they had roots"---tylecodons, haworthias, othonnas, adromischus, adeniums, and--oh god, don't even get me started on pachypodiums! They can be treated as if they had roots IFF they, in fact, have roots. Water-hungry tropical plants, on the other hand, do root best in water and/or wet soil.

Hydrogen Peroxide is also corrosive. Issue with H2O2 is how quickly it breaks down. Once a bottle is opened and some of it is used, even if kept in the dark it will continue to break down (albeit more slowly). Therefore, by a small bottle and use it all within a short period of time. The issue with degree of sterility depends upon just what one is trying to prevent. For fungi and bacteria, simpler, less thorough methods are typically fine. However, with viruses more complete methods may be necessary. With orchids, the main concern is the transmissions of certain plant viruses. Several of these pathogens would not be affected by alcohol or the flame from a butane/alcohol flame. (The latter don't get hot enough.) I typically use disposable razors. They're cheap. Afterwards, I dry them off and toss them in a tin which goes in the oven. Next time I bake, they get "cooked".