The models ID in cutscenes were changed back from using display ID to using NPC IDs in the past (as it wasn't clear how to get the required ID, you couldn't get the display ID with the addon functions and even finding that info on Wowhead required some inspector stuff). The downside is that some NPCs have multiple possible models and a new random model will be selected every time it's displayed.

It could be considered to add an option to use a display ID instead of an NPC ID as an advanced option in a specific step. (This would probably need to wait for a cutscene editor rework with the rest of the pending cutscene changes)