Hello,
Quake Update 1.06 is a progs.dat update --> QuakeC
CycleWeaponReverseCommand is the same as
CycleWeaponCommand only backwards. So it was simply missing in Quake 1.01 ...
It should be no problem to add a reversed function manually, even for an unexperienced person.
What I was trying to say above (but some misunderstood due to my bad english) was that some
engines add a "cycle reverse weapon feature" (can be binded to impulse 12), even when playing with Quake 1.01. Spirit just mentioned one (which seems to be his favorite

).
Regarding
Abyss of Pandemonium:
Open its weapons.qc and you will see that it calls
CycleWeaponCommand () with impulse 10
AND impulse 12. Correct this, so that impulse 12 calls
CycleWeaponReverseCommand () and fix it.
Regarding
Beyond Belief:
In its weapons.qc you will see that it lacks impulse 12 completely. Add it and make it call
CycleWeaponReverseCommand (). Which is, as mentioned above, a reversed
CycleWeaponCommand ().
Have fun with these really great episodes !