There is no reason for the router to exhibit the symptoms you described.
When you change a non-extended networks zone name you must follow these
steps:
1) Set the current status to off.
2) Click the Zone name box for the network you want to change.
3) Select the zone name from the zone names list, there should be only
one for non-extended networks.
4) Click the Delete button to remove the zone name from the list.
5) Type the new zone name into text box and click on the Add button.
6) Save the changes and restart the Macintosh.
It's easy to open the dialog box to change the zone name. Select the old
name, change it in the text box and click Done without ever deleting the
old zone name from the list. This causes the zone name for the network to
not be updated, and the old zone name would be used the next time the
router is loaded.
The only way this could fail is if there is another router that still has
the old zone name or a different zone name configured for this network. The
newly-configured router would then fail with a conflicting zone name
message the next time it loads. It would not fall back to the old zone
name, but would fail and ask you to reconfigure and restart.