I started by defining a v3 hidden service in torrc and running tor, thus creating a v3 private key. Then I commented out the HiddenServiceVersion 3 line and sent the tor process a sighup using kill -HUP processid. The v2 private key and hostname were generated, but the v3 address kept working the v2 address did not work. I then sent sighup again, and this time both the v2 and v3 addresses worked.