I've put instructions for making a startup screen there too. If you want to be able to change what program opens a file, then you need FileTyper , or at least the included AutoTyper program. You may learn something as well. Here are some of my reasons that I can put into words. This is not a complete list.
Information is stored with files that includes an identifier of the application that created it.
Extensions in the file name are not necessary for file recognition. Application locating Using file IDs, the OS keeps track of what applications are on your computer. So you can rename or move them to different folders and they can still be found for the purpose of opening a file. Try this with the Windows registry. It seems like the MacOS was designed from the start with variation in color capabilities in mind.