I don't think I know a single level maker which would like you to take their level, change its tileset, fix and upload as yours. I believe you can't learn anything by such practice. Also most of the levels would lose a lot of tricks, flow and eyecandy because of that, due to specific mask and tiles of each tileset. Example? Diagonal pipes in semi, like the ones below the carrot. Good luck finding a tileset which would keep carrot tricks as they are.