Starsector 0.97a is out! (02/02/24); New blog post: Simulator Enhancements (03/13/24)
Ah, that's a shame. It would be really nice for testing if I could assign a color to see what's populating correctly and what's not. (not to mention making it easier to say 'just go into dev mode and turn off sensors, the X color systems are affected by my procgen code' when people complain). But I get why; it's extremely marginal.
It is a Nexerelin feature. The issue with derelicts is that, besides the Guardian, those ships aren't actually all that good. Remnant and Blade Breaker raids are supposed to be more dangerous than normal enemies and derelict raids would fail at this purpose, unless they used copious numbers of Guardians (which don't seem to be reproducible at all...).