While searching for some edited sprites I stumbled upon this
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View attachment 2536634
And to answer your question: if you want to move to another engine, you'd probably need to recode the entire game from scratch, and nobody is really motivated to do something that hard (though I heard someone tried to do it in Unity but I lost the Github repository)
The only things you can do would be to decompile the game (data.win file), then edit the sprites or anything that you can touch, then "recompile" the game and hope it works well. I'm currently using something called GM Editor to decompile and recompile the game, and also another tool called Altar.NET for decompiling to JSON (so that I can understand better how the animations works and to what some piece of data corresponds to) except this one can't recompile the game back, any other tool I tried didn't work for me unfortunately.
For the sprites, I just use a pixel editor online (do not use MS Paint or it'll mess up the transparency of your file) to make the edits and export them back to PNG. You also have to make sure the size of the edited sprite file isn't bigger than the original one (that's the same for any file from the game because the edited game file shouldn't be bigger than the original one)
Recently I've tried fiddling a bit with the "code" part of the game by using a hex editor to edit some data and the only thing I've achieved was to make some animations longer (or shorter) by basically changing the number of iterations the game does on that animation.
Sorry for the long post guys, I'm usually not the type to write a lot of things but I felt that I had to explain a bit what's happening in my part. I'm probably still missing some details but I hope it was pretty clear.