by Ken Task.
Well, one could do 'exacto-knife' and change values in DB tables ... that's one way.
The other ... truncating all related tables ... moodle doesn't know automated backups have ever run ... like it was the first time. So preferences for course backups (system wide) come into play ... users/no users, events/logging ... how long ... plus, if were me, I'd make sure I had space outside of moodledata/filedir/ where I could see the backup files and their sizes. Got enough space for that?
Best way? Dunno! Works for me! ;)
'SoS', Ken