For trial bicycles there is a technique to improve braking performance by roughening the rim surface using a grinder.
Apparently, this technique is not widely seen outside the trials competition. There are other ways to improve the braking efficiency (better pads, cables, housings and technique) worth trying before messing with power tools. Not to forget that decreasing rim's thickness shortens its lifespan.
I recently discovered (purely by accident¹) that application of a certain kind of household cleaning fluid to the rim surface had improved braking power on a few spots of the rim.
The only explanation I have now is that the rim's surface has gotten chemically etched, which roughened it in those spots. I wonder now if this is another viable hack to try for braking performance.
Is such chemical rim treatment a thing to consider? Is using a sandpaper and roughening by hand an alternative?
¹ I was cleaning a neglected chain from a nasty thick layer of dried teflon chain lube. Apparently, I was not very accurate and a section of the rim got covered by the cleaning liquid. The same liquid has demonstrated to be able to remove anodizing from a cassette, meaning it is quite powerful (base? acid? no idea). I should probably stop experimenting with it…