I tried the method
[serverSettings]
activemods=<mod ID>
without any success myself so I've been trying to do the sergrid.json but I can't be certain what the format for multiple mods is
"ModIDs": "163xxxx","163xxxx",
"ModIDs": "163xxxx""163xxxx",
"ModIDs": "163xxxx"163xxxx",
"ModIDs": "163xxxx,163xxxx",
I'm only running the 1x1 right now so I don't mind the manual edit if I get it in there without breaking it.