Long ago, I succeeded once to cut my own access through SSH to a remote server, after some firewall changes. That of course has required a long trip to the server, for physical access.

However that was good, because after that I have always been extra careful at any changes that could affect the firewall in any way. (That is not restricted to changes in firewall rules, because there are systems where the versions of the firewall program and of the kernel must be correlated, so an inconsistent update may make the firewall revert to its default state of denying all connections.)