Can a seized rear door lock on a 1993 Lincoln Town Car simply be disconnected electrically but be operated manually?

The short answer is no. the actuator is holding the latch in place. If the door can be opened you can either drill out the rivit that holds the actuator body to the door frame or go inside the door and remove it completely. If it can't be opened you may want to go t pull a part or some other help yourself junkyard to get some practice removing the door panel without doing too much damage before attempting it on your own car.

I don't think a bad actuator can keep a door handle from working, they each have their own connecting rod to the lock mechanism. In short, it shouldn't matter if the actuator was hooked up or not, good or bad, the door handle should always still work, unless it too had a problem with it's connecting rod. You may want to check the locking mechanism on your door isn't seized, graphite powder or a liberal dousing with penetrating oil may be in order. (graphite powder is considered batter as it doesn't leave a residue behind to attract future dirt and grime).

Section 01-14A: Handles, Locks, Latches and Mechanisms 1993 Town Car/Crown Victoria/Grand Marquis Workshop Manual DIAGNOSIS -------------------------------------------------------------------------------- Handles, Locks, Latches and Mechanisms Refer to the following Diagnosis charts to service the power door locks and switches. NOTE: Before starting electrical diagnosis, check for mechanical binds by manually operating door locks. Operate lock system several times from each switch, while observing the operation of all door locks. Be sure battery is fully charged. Condition Possible Source Action One Door Lock Does Not Work Latch or linkage binding. Using Multi-Purpose Grease D7AZ-19584-AA (ESR-M1C159-A and ESB-M1C106-B) or equivalent, spray into latch opening and manually cycle ten times. Check for interference around night latch and all linkage. Open or shorted circuit. Check for voltage at actuator connector, operating switch in both positions. Service circuit if necessary. Malfunctioning actuator. Test actuator. Replace if necessary.