as far as i know, you MUST have enemy civilians or other opponent (AI) that is not your ally
after opening cheat menu (alt+F2) go to enemy (civs or ai or other player) veiw (double click on player/enemy witch view you want to enter, they are on top or top-right of cheat menu)
Then you spawn whatever you want and it will belong to that enemy and only then you can go back to your view and attack those units with your own units
I believe you need to select a map with hostile civilians on it. Or just spawn an AI in one of the other spots and kill it off before it starts building.
Peace through superior firepower. [Total Biscuit, comparing FA to SupCom2] "The scale and the sublime nature of the economy was ruined with Supreme Commander 2, which I absolutely despised. Oh god, I hate that game so very much."