If you use the save of the version 051 in the version 041 you can bypass some limits and even beat the game (you can only get the bad end and the normal end)
Just replace the save file. For example in 051 you can get throught the bridge to mirror castle but there is a placeover barrier. That barrier doesnt exist in 041 but you cant get past throught that purple square things in the middle of the bridge.
Yeah, no problem. The only thing to keep in mind is that if you want to advance in the game in previous versions, you will have to add the image files, otherwise it will give errors (simply copy any file from /img/pictures/, make a copy of it and rename it with the missing file as many times as the game asks for it).