Never something I ever try to do, but sometimes you don't have a choice. If it's warm out, and it's a drizzly rain, then you're probably OK, if you don't mind getting damp yourself. But a heavier rain could be detrimental to a colony on keeping the bees and brood warm.
I didn't have a choice, I had to open the hive and do work after a cutout. So I rigged up a 10'x10' canopy to keep the rain off of me and the bees. It was about 70 degrees and a steady harder rain all day. There was no waiting it out. The canopy worked great to keep me and the girls dry, but had some flaws with the bees wanting to gather up at the peak.
Still, it all worked out and the bees looked great, so that's a happy ending.