[USiBqidmOOkAqRb]

Yes, but, as the name implies, only once, and selectively at runtime. If you have a service and issue sv once on it, it will not be restarted, but its configuration is not changed so it will run normally after system restart.

[XorNot]

That's a one-shot service[1].

RemainAfterExit=yes is what achieves the effect (i.e. if the process terminates it is regarded as still active for system-dependency purposes / status unless you purposefully mark it otherwise).

[1] https://www.redhat.com/sysadmin/systemd-oneshot-service