I would think so, though I personally have not done so.

The vacuum elements inside both front doors also has the electric switch
that turns on the vacuum pump (inside the spare tire compartment).  The
wiring probably go along the outside edge of the passenger side floor
(or working directly at the pump).  The trick is to figure out how to
send the correct signal.  I believe it is to reverse the polarirty of
the voltage.  Remember that it is vacuum to lock the door and pump to
unlock.

Yes, any aftermarket alarm installer can install the alarm and hook up
electrically. No need for door lock actuator as your model year is all wired
up electrically in addition to vacuum pump.

Older model... 85 and older need the door lock actuator to work.

There are after market remote kits for w124 and w201. You just connect a
few wires that go to the vacuum pump underneath the back seat. I
installed two of them in my w124 and the GF's w201. They work well. I
haven't seen any available for w126s but perhaps it's just a matter of
figuring out the correct wires.

Ximinez