Hej Dannan,
your approach is correct. I've added some stuff on my local lif server too. At first assigned ids starting from 1153 (current max object id is 1152), ingame check: passed.
Then I've added an object with the id 2222 ... and the ingame result was a -surprise- Wooden Scout Tower
It took me awhile but I've figured it out.
If you add an object with the id 2221 you'll get a castle wall, add an object with the id 2178 and you'll get a 'primitve sickle'. Don't forget these first 30 pseudo-objects (system objects, gameplay objects, inventory etc.)
2178-30 ..
so the current max. value for a valid ID is 2048 (and useable new objects)
I guess it could be a mariadb configuration but I've not checked it yet.
That's it