Editor-placed package should have its AI stack read from ACSC in .ess files
It seems that in the original game the number of the package stack an NPC is on is stored in a particular hex value under an NPC's ACSC record.
This value is independent of the AI type. i.e. if you have an NPC with Wander followed by Follow followed by Wander, the value will be 00, then 01, then 02, then 00 again when it starts over at the first Wander.
In morrowind.ini, change
and load the attached .esp. The NPC in the room has no equipment, abilities, etc. but is full of 1-hour 0-radius wander packages. Save the game, then rest (fast-forward) for an hour, or as many hours as you like, and save again. Look at the two .ess files in a hex editor and note the different value. (For me is at offset 00011DB0) You can search for the npc's name "aaa" to find the general area of the file. There are also differences under "ND3D," but I don't think these are related because values under ND3D will change even the NPC has no AI packages at all.