Place assets at known coordinates during build (not runtime)

I make visualizations of real life projects so have locations of items from cad drawings.
I know how to manipulate things to get coordinates for unity, and would expect I can script the placement of them in my world using that instead of drag and drop by hand.
All the examples seem to be for runtime though to spawn stuff here or there.
What is the way to do this at build time - meaning, in the editor, not at actual game compiling...
I'm sure its simple, just eluding me.
thanks

 

So I realized the keywords to search on this are "editor script". Sometimes lingo is half the battle.
thx