Both values this relies on are Simple Data in eud_book - Units.dat's Staredit Availability Flags and Unit Dimensions - which is the safe end of the scale on Remastered. The source is 2020 era, but these two check out.
Some units do not appear in the editor's unit list. They are hidden because their Staredit Availability flags say so, and setting bit 0x02 brings them into the list.
Terrain refusing the placement is a separate problem. Setting the building dimensions to 31 by 31 gets it past the editor's terrain and occupancy check; put the real size back afterwards.
Never set dimensions to 0,0,0,0 - crash list #42. And a building straddling or outside the map bounds crashes as #1 and #46: bypassing the terrain check also means losing what the check was protecting you from.
- Scarabs and Interceptors still cannot be placed this way.
- Minerals and geysers always end up owned by P12 however you place them.
- To change the colour, create as another player then fix the owner in the structure offset - but if that unit can later be removed or destroyed this crashes, as #22.