Well... yes. You need to get PYMS (no idea if the other AI editors support extended commands). Probably this version:
https://github.com/neivv/PyMS1. Get the scripts\aiscript.bin and scripts\bwscript.bin from the game archives (PYMS provides clean default versions methinks).
2. Edit one of the blank scripts to include the liftoff order for the relevant buildings, and save them.
3. Edit the map specifying to run that AI Script (most of those only run for computer players, with very few exceptions) under the conditions of your choosing. Obviously you need to do these two parts concurrently as you need to specify the locations where the building is, and where it should be landed, as I had written before; you need either the exact location IDs that are made obvious only after you've created these locations in the editor, or the specific coordinates).
4. Build a mod with AISE present (I'm not sure where to get a compiled version as Neiv's there only seems to be the source code on Neiv's github. The exact procedure depends on which version of SC you're using. I can only speak for Remastered. The modloader SAMASE has its own thread here:
http://www.staredit.net/topic/17430/ If you use it, you need to create a mod with the scripts\aiscript.bin, scripts\bwscript.bin, and samase\aise.dll. Also add a plain text file called 'plugins' to the samase\ folder containing the names of all the plugins you're going to use, in this case just:
samase/aise.dll
5. Patch the game.
P.S. In my case the landing script invoked during a mission looks like this:
# stat_txt.tbl entry 1348: Brood Wars Protoss 1 - Town D<0>
PB1D(1348, 101, bwscript):
issue_order(Land, 1, Terran Command Center, Loc.63, Loc.37, Any, 0)
issue_order(Land, 1, Terran Barracks, Loc.63, Loc.42, Any, 0)
issue_order(Land, 1, Terran Factory, Loc.63, Loc.53, Any, 0)
stop()
It replaces a blank Brood War script, of which there are 55ish, so you can write literally as many of them as you need. However, if you feel like conserving script slots and not doing separate ones for every little action like this, AISE also allows to evaluate death counters and jump accordingly, so setting a particular death counter through triggers right before a script is run and evaluating that same counter in the script's beginning allows for amazing branching.
The guide for basic (Starcraft and Brood War) AI commands is found here:
http://pr0nogo.wikidot.com/rs-aiThe guide for extended (AISE) commands is found here:
http://pr0nogo.wikidot.com/rs-ext-aiI should note that issue_order is a goldmine of potential uses as it solves the long standing gripe of map authors being unable to issue any command other than move, attack or patrol to units. Even though it's done in a rather roundabout way, it still opens a new level of customizability when doing triggers.
Trial and error... mostly error.