Ah, someone else has picked up my favorite game. The user neverobsolete created a wonderful editor for it called NinJax, which you probably have used. He modified it so that you could change the physics properties of different tiles (i.e., whether the player passes through, can cling or climb, stand on, etc.). I don't know if that version was released publicly, but I could probably send it to you if you're interested. He was a very helpful and knowledgeable fellow.
I had planned on making the game much more difficult, with more sophisticated and dangerous AI, and greatly expanded player abilities. I also wanted to make the level progression non-linear, where the player can choose which level to play next, and completing a level unlocks some new ability. This isn't hard to do with the "warp" tiles that move you between screens. I got it to the point where pushing select chooses different Ninpo (shuriken, firewheel or windmill star), and reaching certain score thresholds allows you to heal yourself, temporarily run faster, or become invisible. I was just moving into level design and AI when life overtook me.
I wish you the best of luck. Please keep us posted about your progress. Your hack sounds ambitious.