While any division is locked, you can't save changes to the round's settings. Once the round is launched, you also can't remove teams, add divisions, unlock divisions or change the dates. Make these changes between rounds instead.
After you lock a division
The round's settings can't be saved. You'll see "Cannot update round with locked divisions".
Before launch, you can unlock divisions to change settings, as long as none of their matches are scheduled. Unlocking deletes the division's matches, which are created again when you lock it.
You can still change these on the round's Settings tab:
Scores affect players' levels (applies to scores reported from then on).
Which courts players can book on general availability (applies to matches booked from then on).
After you launch the round
You can't add teams to a division, because every division is locked.
You can't remove a team. Removing is also blocked while its division is locked or it has scheduled matches.
You can't add or remove divisions.
You can't unlock a division.
You can't change the round start and end dates.
You can't swap players in a team that has an upcoming scheduled match.
At any time
A score can only be reported once the match has started.
Good to know
Check settings, teams and divisions carefully before you lock the first division.
For the next round, you can change all settings before locking. See "8. What happens when a league round finishes?".