“so I suppose it’s safe to swap them in and out if you want to run different OS distributions at different times on one Pi?”
As long as the Pi is off, yes. I do it all the time. I re flash the cards all the time too. Been using RPi since the beginning and never broke an SD card with one. But then I only use scandisk cards brought from outlets I trust, IE direct from Amazon.
2 golden rules: 1 Shutdown the RPi correctly, don’t just turn the power off. 2 Don’t remove the SDCARD with the RPi powered on.