Ok, so now I've hacked things in a bit more... suitable way... and I have cracked the problem entirely.
First off, the designation "sc_freighter" is referring to the line type = FREIGHTER in Shiparch.ini. Any time an Encounter refers to freighters, it's going to:
1. Look at the available Loadouts, which are called by the Group assignment.
2. Look for any ships in the Loadouts that refer to FREIGHTER, such as Pi_Freighter (the Mule, which started this whole mess).
3. Assign one of those ships, based upon the Encounter difficulty and type.
This requires the engine to search through the local Encounters, which are set up for each Zone in a system, then to refer to faction_prop.ini, which in turn refers to npcships.ini, which ... finally... refers to a given ship hull and a Loadout, which is specified in Loadouts.ini.
This is an incredibly cumbersome and over-complicated way of doing things, imho, but it's the way that the game engine finally figures out how to randomly select a FREIGHTER. Then the
behavior ... and this is what I was trying to solve, so this was the important part... is controlled by the TYPE.
So, as a less-kludgy, functional solution, I have changed all FREIGHTER entries in my shiparch.ini to CRUISER. This makes them plenty violent... they will NOT try to escape via Cruise, which is basically what I needed to have happen here.
Now, they didn't show up in Encounters until I started changing lines in them from sc_freighter to CRUISER. Be aware: this
will cause Factions with CRUISERS listed in Shiparch.ini to start fielding... you guessed it... CRUISERS. Which is actually kinda fun, if you like watching cruisers kick some boo-tay
In my case, it means that I'll have to change all of the CRUISERS to use the Battleship or Gunboat type, eventually, since I do want to preserve some available hierarchies of powerful warships, and I do want to be able to write Encounters for various Factions that allow them to field warships.
Now, for the (hopefully) last major icky technical challenge: how to get ships to ALWAYS spawn at a given height level. This ought to be... tricky. I'm looking forward to it