@ejms07 : the problem with modifying the galaxy generation algorithms of the Stellar Forge is that changes there will almost certainly alter every generated system, or even "just" vast amounts of them. Even the occasional small bugs would reroll specific systems, as happened with Beagle Point, 3 Geminorum, and so on. Many players have voiced that they'd be quite upset if all their discoveries were gone, and then imagine how the player communities inside the bubble would react if the inhabited systems were all rerolled. I'm by no means an expert on the BGS, but I assume it would crash and burn anyway.
As for inserting star systems into the current galaxy, the problem there is that the mass for the star system has to come from somewhere, because the total mass is already set. So even in the simplest scenario, you'd have to remove some mass from nearby systems (quite many of them, in fact) to be able to add the new one, and then those systems would be rerolled as well. Plus we don't know how exactly that would work, maybe the changes would ripple on even farther. Either way, it'd be a lot of work and plenty that could go wrong, for very little gameplay benefit.
Now, they could do what they did for TRAPPIST-1, and delete a procedurally-generated Y-class brown dwarf in the same general vicinity of WISE 1534-1043, and replace it with a new Y-class brown dwarf named WISE 1534-1043. But that's an awful lot of work for them to do, just to delete one boring old y-class dwarf and replace it with another one that's exactly like it. There are plenty of other "stars they ought to add to the game" that have a higher priority than this one.
For TRAPPIST-1, it wasn't even that: instead, they took the original PG system (which was Core Sys Sector XU-P a5-0), renamed it to TRAPPIST-1, since both its position and mass were remarkably close to the real system's. Then they manually edited several of the generated bodies to be closer to the real exoplanets: these edits were quite evident because they messed them up, and for a short while, these edited planets were bugged. (Couldn't be targeted, didn't show up on the system map.)
Here's how it was:
