this isn't something you do 10 years into a game's lifecycle.
engine is the pretty much the foundation of the game. you will have to dig up the house to rebuild the foundations - it's an absolutely monumental undertaking. literally every facet of the game interacts with the engine in some shape or form. you would have to edit and change every single facet of the game, it's essentially a re-write of Elite Dangerous.
in which case you might as well just make the sequel!
engine is the pretty much the foundation of the game. you will have to dig up the house to rebuild the foundations - it's an absolutely monumental undertaking. literally every facet of the game interacts with the engine in some shape or form. you would have to edit and change every single facet of the game, it's essentially a re-write of Elite Dangerous.
in which case you might as well just make the sequel!