Reverse engineering a game engine?

I dont know if that title fits my question but here it goes. Rayman 2 The Great Escape is one of my all time favorite games. What would it take to make Rayman 3 in the Rayman 2 engine, Or to make a custom level in the engine? Is that even possible? Would it be possible to make custom levels? I'm assuming it would be extremely complicated and possibly borderline impossible. These are just some thoughts that i've had for awhile. I Have no idea how any of this would work so I thought Id throw it out there. I really have no prior knowledge on any of this. Hopefully I have wrote this in a somewhat understandable way. Really what it boils down to is "Is it possible to make your own content in Rayman 2?" If you dont understand what im asking ill try to rephrase the question. 

If its a game made in an unknown engine there is a way to port it over to UDK