I didn't realise this at the time of opening this ticket but according to Arkensor:

Not editable by script, configured at loadtime through the prefab on the map. You may request script api via feedback tracker if you can present a usecase that shows the need for it

After some assistance digging into this issue on Discord from reyhard, it turns out this problem is due to the long path the original mod had.

After further investigating I found the same error occurs when running PeerTool in the utility mod (RLM) directly. This mod is nothing more than a single new class and some new prefabs. No overrides or anything, so this should not be possible.

This appears to be fixed now in 1.3

The issue seems related to my script-spawned vehicles being added as a child node of the spawner entity (so CE can track removal and enable spawning at that point again).

Edit: nevermind i thought this ticket was for Reforger