I'm not sure if this has been posted before, but I "discovered" a way to place extended units in starforge without having to manually go into the unit porperties box.
First go to terrain and open the Master Tile Palelette.
Then using the dropdown menu at the top, switch modes over to Units, or sprites (they work too).
Then select a square of terrain from the tile palette and place it on the map. Voila, it places a unit instead! This can be used for the normal units by placing from the first tiles, and then the extended units after that. You have to keep in mind that the units start at 0(terran marine), as the first square of null terrain, and then their are 16 units in that first row, (16 tiles of null). The second row then starts at 16, terran ghost. It goes like this all the way through the palette.
Somewhere between 2.0 and 2.2 he fixed that. I used to use this in Sf1.0 before I switched to 2.2. I also on other comp had 2.0, but never tried.
I am going to suggest making it so that the Master Pallete refreshes itself when you go to Units or Sprites so you can use it that way.