I've found a way to basically remove everything so that you can place stars centred around Sol's location without existing stars getting in the way. This is how to do it (warning - it will remove all everything in the Milky Way so only do this if you're OK with that!).


1) I copied everything from the planets and stars folders in catalogs.pak to addons/catalogs/planets and addons/catalogs/stars respectively. (you can open pak files in a zip program like Winzip, Winrar or 7-zip)

2) I then renamed the catalogs.pak in Steam\steamapps\common\SpaceEngine\data\catalogs to catalogs.old to stop it loading.

3) I deleted all the copied files in the addons/catalogs/planets folder except for:
SolarSys.sc
SpaceEngine.sc 

4) I deleted all the copied files in the addons/catalogs/stars folder except for:
SpaceEngine.sc
Stars.sc
Stars-fix.sc

5) I edited the planets/SolarSys.sc file and replaced the Star "Sun/Sol" entry with the code below and deleted everything else after it:

6) I edited the stars/SolarSys.sc and replaced the StarBarycenter    "Solar System" entry with the code below and deleted everything else after it:
7) I had to keep the Stars-fix.sc file because deleting that file or removing stars from it seems to make SE always crash on loading, but keeping the file and editing its existing contents doesn't cause it to crash. Something in here must be essential but I couldn't figure out what it was - but replacing the AppMags of all the stars with 20 and increasing the distances to something like 5000 basically turns all the stars invisible and moves them all out of the way. (You may need to use some fancy search/replace text editing for this). So this seems to be a decent workaround for now.  I've attached the edited file below so you can use that if you don't have the fancy editing methods. 


And that's it, it should work. You're left with a black hole sun with no planets at Ra 0, Dec 0, Dist 0, and all the other stars in Stars-fix are out of the way and invisible but now you can populate an empty universe (you have to turn the galaxy display option off too, it still randomly generates those)! I made a MyStars.sc with a Mono star (from the manual) and that shows up fine and even has its own procedurally generated planets. 


All the procgen stars and galaxies outside the Milky Way still exist, but it appears that there is nothing in the Milky Way itself after this (except the hidden/invisible stars in stars-fix.sc, Sol, and whatever you add in your custom.sc). 


NOTE: If you want to revert back to normal SE then delete everything made in the addons folder here, and rename the catalogs.old in the data folder back to catalogs.pak and that should bring it all back to normal. 

You may be wondering why anyone would want to do this - this allows a user to import their own universe (i.e. from their own .sc files) and place objects in it using RA/Dec/Dist coordinates without anything else getting in the way. 

This is a sphere of stars I made using my own procedural system (outside SE) for an RPG setting, that I converted to SpaceEngine format. There are 15551 stars in a sphere about 186 ly in radius around a RA 0/Dec 0/Dist 0 central point (I ramped up the star magnitude to 19.99 so they're all visible).

We already did something like that in the old forum. [Community Addon] Custom Universe

And now anyone can in the latest SE!

Did you have the same issue with the Stars-fix.sc file there? There must be some object in that file which is somehow critically important for the game's stability so that it'd crash if deleted, but I couldn't figure out which one it was.

It's been a while since we did this. I don't remember any details.

So you basically created your own custom night sky for an RPG setting? Wow, that is commitment. I'm impressed 

evildrganymede:

There must be some object in that file which is somehow critically important for the game's stability so that it'd crash if deleted, but I couldn't figure out which one it was.

It probably isn't a specific object that's important. More likely it is just that SE has an object to load. SE probably needs at least one object to run through its boot process. 

Basically yes . I would have liked to have just been able to place the stars in their own cluster far away, but there's no way to make a new co-ordinate origin in SE. So the only alternative was to remove everything that was there already and replace it with the new stars. 

Ultimately I just want a way to visualise all the systems that my generator made - i've got the stars in, now I just need to figure out how to convert the planets.

 but there's no way to make a new co-ordinate origin in SE

You know I've wondered about this myself with my own planet generator. I always thought it would be cool to generate SE systems around a point and would love to make that an option, but I don't see how to do it without some serious maths. Really I wanted to generate nebula and things on a grander scale than single solar systems. 

An empty universe with only a few galaxies. And a somewhat modified solar system.

When I attempted it, the Milky Way and, I presume, other known galaxies did disappear, but the procedural galaxies are still there. Is it possible to make them disappear as well?
Also, a question about adding procedurally-generated galaxies: once you try to create a galaxy using this method, will SE procedurally generate the stars and systems within it too? 

When I attempted it, the Milky Way and, I presume, other known galaxies did disappear, but the procedural galaxies are still there. Is it possible to make them disappear as well?
Also, a question about adding procedurally-generated galaxies: once you try to create a galaxy using this method, will SE procedurally generate the stars and systems within it too? 

So, from my experience, getting rid of procedural galaxies completely can be a bit tricky. You might have to tweak some settings further. As for your second question, yep, once you create a procedurally-generated galaxy, SE will handle the insides, generating stars and systems for you.