The default night sky is a 512x512 texture, is there a way to replace this with the SpaceBox Dark materials? I really want to customize my night sky to get something a lot more beautiful while keeping all of the other changes it goes through in the day and night cycle.
Yes, first make copy of that blueprint under different name.
Then make local copies of all textures and materials it uses.
Then edit that night sky material.
I advise making local copy because i am not sure what happens if you create new level and it tries to place own (default) version of that blueprint into your project.
So better be safe and work on copy with different name.