In the hopes of preserving all the programming that we'd recorded on the prior install, I chose to upgrade, rather than reinstall. That proved to be only partially successful. The raw files still live in
/myth/tv, but MythTV no longer knows anything about them. When I have time, I'll try to figure out how to move the videos so that MythVideo will recognize them.
I also took the effort to migrate my listing service from Zap2IT to SchedulesDirect. The project leader for KnoppMyth posted the procedure on the phpBB forum.
Signing up for the service was no problem, and the manual upgrade procedure went fairly straightforward. The only two hiccups I have are with the channels recognized by MythTV for the input source. After doing the upgrade and setting up MythTV to use my SchedulesDirect account, the channel scan failed to eliminate the channels that I don't have. The other problem was that the names for the channels are all listed as "Adding Channel". Both problems are being encountered by others, per the postings to the forum.
If I find any solutions besides just manually correcting, I'll post it.