Enabling and disabling maildir.synchronize_flags

[dm-list-email-notmuch at scs.stanford.edu]

Sorry if this question is answered somewhere, but I'm wondering:  What
is the best way to enable and disable maildir.synchronize_flags?

It seems that disabling it should simply be safe.  But re-enabling, one
risks losing tags, as the next notmuch new will cause old maildir flags
to override the xapian database.  So that suggests something like:

   notmuch dump > backup
   notmuch config set maildir.synchronize_flags false
   # Do I need to run notmuch new here?
   notmuch restore < backup

Is that safe?  The man page suggests one additionally need to run
notmuch new before running notmuch restore.  All of this is pretty slow.
Is there a more efficient way?

A one or two sentence clarification in the notmuch-config man page might
be helpful to people contemplating playing with this switch.  The
default is on, to I suspect it costs a lot of performance.  I've been
afraid to turn it off for fear that I won't be able to undo this
cleanly.

Thanks,
David