How to associate a Windows application with a particular file type but share that association with other applications?

Question

If I create a new app, and associate with, say, the .xml file extension on a particular computer, when someone double clicks the .xml file, it will launch my app and pass the fi

Answer 1

In Windows Explorer click on Tools->Folder Options->File Types. By clicking on "New" or "Advanced" you can create/change your own application associations with various file types that will appear when you right click on the file.

EDIT: I don't know if there's a stub that redirects specific files. You can check My Computer\HKEY_CLASSES_ROOT in the registry and see what it's putting in there.