You normally will need to restart services such as SMB when making configuration changes It only takes a few seconds to toggle off the service then toggle it back on, and it is how the service reads the new configuration. This is normal and applies to most systems and middlewhere like Truenas, Some systems will automatically trigger a service restart (QNAP will) on save of a configuration change.
I don't use a Mac or TM, but my understanding is the backup process will resume where it left off either when the share is remounted on the Mac or at the next run. You should also be able to pause then resume any backups.
Service restarts and even server restarts if necessary are done all the time even during production so it's not usually a big deal.