I have tried to remove bearings before.
I tried to make a jig and use a press, I got bored after two evenings and gave up. I also tried to cut the axle shaft between the bearing and flange - Futile, The axle is a high quality steel and the band saw barely scratched it. So I used a cut off wheel, the heat from cutting the axle burned up the rubber skirt on the outside of the bearing If you have a full shop complete with liquid nitrogen, I think you can do it. Otherwise, I would have to be in the middle of a third world country with no other options before I would take the time and effort to try to remove another bearing and retainer without destroying them.
The cheapest place I have found to buy rear wheel bearings is road less gear even after shipping.
A side note, for your spare axles, you can cut the backing plate off and only leave the center portion the same size as the SJ410 bearing retainer and use that.
We had to do that for Zukiman out in the field last March. Fortunately we had a member with an air cut off wheel to cut Lorne's backing plate down to make a retainer.
My spares, I took the bearings off and carried them as shafts only with a bearing and retainer in the tool box - nice clean and dry. I also carried a section of pipe to drive the new bearing and retainer on in the field. That also offsets costs by allowing you to purchase one bearing and retainer to use for either side when needed.