safe to run "ctl_cyrusdb -r" while server running?

[James Ralston]

I need to clear the \Reserved flag that was set on a mailbox (because
a renamemailbox operation failed halfway through.)

Is it safe to run "ctl_cyrusdb -r" while the server is running, or do
I need to shut down the server first?

If the former, will running "ctl_cyrusdb -r" cause any impact on
clients?  E.g., will no one be able to create new mailboxes while
"ctl_cyrusdb -r" is running?

(I'll submit a patch to update the man page for ctl_cyrusdb once I
have some definite answers.)

Thanks,
James