How do city-state starting locations work?

I'm wondering if I can make a specific civ like Japan or Polynesia (or a custom island civ) start out on its very own island, but not too small either like 1 or 2 tiles like some city states start out in.

If it's not possible to make a civ start out in small islands, will it be possible to do that via LUA? If so, how hard is it? I know that the Inuit Civilization by Colonial Legacies are able to make the Inuits start out in the snow with a looonnnggg lua file.

Is it also possible to use lua and alter the starting location's tiles? Like place ocean/water tiles around the city's vicinity before the game "starts"?

Easiest way to start a civ on a small island would be to loop all the minors, analyse where they are starting (area id, number and quality of tiles in area), pick one, and then swap the starting location of the major civ with that of the minor civ - see my "Maps - Rotate Start Position" for how to do the last bit.

Suspect if you try to modify tiles after the map has been generated but before the game "starts" you'll run into the usual terraforming issues - ie 3d map won't update until save/reload, by SV map will update immediately

Thank you very much!