Yep, go to starsector-core > data > campaign > terrain and replace 'hyperspace_map.png'. I recommend making a backup of the original just in case
If you're making your own, black = empty space and white = hyperspace clouds. The dimensions don't have to match the original but things can look weird depending on whether the new map is larger / smaller
Some mods overwrite the hyperspace map (adjusted sector, mainly) so depending on what mods you're using you might have to replace it there instead