These are the lines that I use to turn it off:

jug_trig = getEnt("specialty_armorvest", "script_noteworthy");
jug_trig disable_trigger();
jug_machine = getEnt("vending_jug", "targetname");
jug_machine setmodel("zombie_vending_jugg");

The trigger correctly disables, but the machine does not change its model back to its "off" state. Why is that so? Thanks in advance!

I believe you did set the model, but, since you didn't delete the last one, they stacked together. You need to add a delete (zombie_vending_jugg_on).

Change
jug_machine = getEnt("vending_jug", "targetname");
To
Jugg_Machine = getentarray("vending_jugg", "targetname");
Edit: if done this way
for( i = 0; i < Jugg_Machine.size; i++ )
Jugg_Machine setmodel("zombie_vending_jugg");

This is from the _zombemode_perks file. So basically you just needed 1 more 'g'. But You can try GetEnt (May or may not work). However this is what it was in the script to turn it on.
You also have the sound and fx that play but dont remember how to turn them off/disable them.