Just a quick experiment
Before

After

Looks great. Will the soldered slot hold up to use?

I used what I have, tin based so it’s soft, I think next time I’ll try something harder. Just a fun little experiment, but I do like the results!

I doubt it, but it looks good.

I suspect it will make TIG welding in the future somewhat of a challenge.......

That was my thought. If you or anyone else ever decided to TIG weld the heads and redress and cut new slots, contamination from any residual solder could be a problem.

The burrs around the screw slots in the before photos looked as if they could have been improved a lot by peening the displaced metal back toward the slot, and then dressing with a screw slot file. Doing this requires removing the screw, clamping it in lead padded vise jaws to protect the threads, and very carefully using a small hammer and punch to peen the metal back in place. Naturally, this may not be worth the time if you can simply find a correct replacement screw.

It’s hard to see, but there was too much metal missing to peen it back. Fun little experiment, I was able to redo it in silver, still soft but so far so good till I get a replacement!

I don't know if it can be done in this situation and not saying it's a good gunmaker option. If peening and dressing leaves a workable screw, a shim can be made to bump the head of the screw back out to where it looks right. It's a pain to make a thin washer, but I've done it a few times.

I like the shim washers used to cure end shake on a revolver. Very thing and easy to trim.