Eh. Pet scripts might need source edits to work properly anyway.
I believe Admiral once mentioned an Eclipse member who was able to successfully create a functional pet system by only using Sadscript. Anyway, I agree that editing the source would enhance the capabilities of a pet system and also make it easier to create one.
Back on topic, maybe editing something about placing NPCs on the map in the “Properties” section of frmMapEditor.frm might help prevent your run-time error problem from occuring. It’s possible that the game may be trying to render the extended capacity of NPCs per map that you assigned it when the map editor has no slots to compensate for the addition.