Instead of drilling out (4.5mm or 3/16" drill) and replacing with a rivet, you can replace with a M4 or 8-32 (or maybe even 10-24) bolt and nut. I found the rivets on my bed were a bit loose when I got the printer, and it made keeping the bed level impossible, so I replaced them all with M4's.
You should be able to get in from the sides to do this job, but ideally you should remove the bed and do the drilling etc. on a workbench. If you do, maybe worth swapping out all the rivets. I did, they were all a bit suspect on closer inspection!
SD3. Mk2b + glass, heated enclosure, GT2 belts, direct drive y shaft, linear bearings, bowden-feed E3D v5 w/ 0.9° stepper
Smoothieboard via Octoprint on RPi