Well in the current status of the code, -tweak-labels will only sync-back if
1 - You have globally set `sync_back_to_maildir` to `true`
2 - You pass it the option `--sync-back`

So considering an example (my case) where I have set `sync_back_to_maildir` to `false` and set it to true per my gmail case, I will have to temporary set `sync_back_to_maildir` to `true` to be able to use the sync-back feature for any of my sources that have sync-back set to true.

Let me try to come up with a different approach that honors the sync-back value of the accounts