I'm sure most of you already know this, but in case you don't...

I always thought there was no way that the computer player could lift buildings without modding the game, but it turns out that there is a script which is capable of doing it - at least with regard to Command Centers. I have discovered this by accident while working on a map: I had intentionally placed a doodad on the right of a Command Center to prevent it from adding a Comsat Station (as an alternative to disabling the technology), however as soon as the map started and the script was executed, the Command Center lifted off and flew to a suitable location, where it could build the add-on. I have not done further testing with other buildings, but I thought this might be of some interest, even if its use is quite limited because you can't tell the computer where to relocate the building, it will decide by itself according to the terrain and map design.

The script is "Terran 10 - Confederate Towns" from the deleted mission Operation Silent Scream, and it is also notable for actively using pre-placed Bunkers without the need of a dedicated "Enter Closest Bunker" script.

It's nothing specific to that AI script. Any script that tells the computer player to build an add-on will relocate the building if the build space is obstructed. Same with bunkers; it's normal behavior for Terran scripts that make use of guards to place them inside bunkers if they're present near the guarded area.

Ok thanks. Strange I didn't notice this before LOL. About Bunkers, it doesn't seem to be limited to the units nearby, as I saw a Firebat walking his way through half of the map in order to enter a very far away Bunker.

That's just the "guard shuffle" as the AI doesn't care about distance when assigning guards, mostly apparent at the beginning of maps with preplaced brigades and multiple bases. It merely decided to make that Firebat a guard and assigned it to that region across the map, and ordered it to enter the bunker as one was near that region.

Well that's not quite right, the "guard shuffle" is not really "guard" related - it's guards turning to military units that get placed by defenseuse_
Likewise when units from faraway enter bunkers they're most likely not guards, they're military defenseuse_ units that the AI requested in this region (and pulled since military is also a valid target for entering bunkers)

Oh, I was actually talking about defenseuse units the whole time, but called them guards by mistake.

Oh I assumed guard-guards since you mentioned using guards to fill bunkers (since positioning guards around bunkers would be vaguely the best way to keep them filled, as much as SCAI can anyway)