There is soem kind of way to edit JJ3 actually.
Basicly, if yuo have the unfinished demo version, you are in lukc and can have some fun with it.
If you have unreal, JUST unreal, then listen to this:
JJ3 the unfinished demo was previously made by Unreal Editor! I have tried to extract the whole demo into a Unreal Editor basicly, and it worked!

Right now I have each graphic and game command for JJ3.

my plans for the future: To finish up the lab level of JJ3 using very simular graphics I make and finishing the Demo version.

So far I have made rat with lab coats as the first enemy you see after you take a purple gem and teleport to the lair.

Fun!