Well I did create an esp using the script to convert a json file to an esp and it didn't work correctly. It only moved the vanilla items to the esp, and created unknown references for any mods. When I load the installed the mod into a semi test game the result was as you might expect. Vanilla items transferred correctly but nothing else. They were some other oddities with the settlement (in this case Red Rocket) but that could be expected. Also loot noted a circular reference in the esp, which I could not visibly find. I am going to try a settlement where I have only 1 or 2 mods installed and see what happens. It could also be that I messed up the Red Rocket Settlement altogether before using transfer settlements.
The preliminary problem with converting the json file to esp appear to be esl files. The Form ID's appear to change even though no new mods have been added/deleted/reinstalled. It appears that this might happen at the script level. It also appears that it does not affect esm files. This could be because the .esm file I tested load order is before the .esl file. More testing needs to be done to confirm. Note; all creation club files are mostly esl files (for me this is a huge issue).
Over a year ago I thought I tested with a .esl mod and it worked fine. It was on the previous version of fo4edit so I will rollback to that version and try again.
Otherwise esp and esm files works as they should. I have tested with 19 mods installed and they all moved over.
My Red Rocket Settlement was a poor test because it was already messed up
Further investigation into recreating previs/precombines requires that the objects reference needs to be removed from the workshop. It was suggested that this could be done by removing the workbench and then adding it back. At what point you have to create previs and precombines is not clear.
If anyone is interested in step by step instructions on how to create an esp from a json file I will be happy to supply them, but I caution you do not put this in a game that you are currently playing. Use a test to check results first. Should you follow the steps and destroy your current game that you are playing, the fault is yours, not mine.