These are the locations of npcs that I could find.

The images are in order from bottom to top for some reason.
1: Choose an id above 1000 that isn't taken by another mod or map. To check if an id is taken, go to the spawntables tab in the workshop tab and type the chosen number in the top text field and click "view". I would check 16000 and 16050 and 16000 to make sure that they are available.

2: In the map editor in the in the legacy spawn text field, type the chosen ID (16000 in my case) and click the text that says "legacy spawns"

3: Navigate to the map folder of the chosen map. There should now be a folder titled "Exported_Legacy_Spawn_Tables". This is where it exports to (obviously).

4: Open this folder. Inside there should be another folder labelled "Items". Remember that this is there for later.

5: Navigate back to the main map folder. Create a folder called "Bundles". Inside this folder, create another named "Spawns". Now copy and paste the "Items" folder from earlier into the spawns folder.

6: The game will need to be restarted now. After the restart, go to Workshop then Spawn Tables, and type in 16000. Now you should see the spawntable info.

7: If it worked, you should be done and now people can edit the spawns so they can add modded items into the spawntables, or edit them.

This church had an apartment complex inside it. I have since removed it but that is only on my end.