/etc is writable, so no reboots are required. That said, /etc is treated in a special way and each deployment will have its own /etc, based on the previous one.
So if you make changes to /etc then revert to a previous deployment, your changes will be reverted as well. But if you make changes and upgrade (or do whatever to create a new deployment), your changes will bu preserved.
I always try to consult the man pages for these kind of questions (you can search by typing ‘/’ in the man page). Here’s what the systemctl manual has to say in the specifications for the
--force
option:Note that when --force is specified twice the selected operation is executed by systemctl itself, and the system manager is not contacted. This means the command should succeed even when the system manager has crashed.