In short, create a key (notepad.exe) under HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options (in 64bit system it is HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Image File Execution Options). Create an string item named Debugger, put in the path of your favorite editor.
But wait, it's not end yet. Your editor need a special treatement, e.g. you need special version of notepad2.exe from http://code.kliu.org/misc/notepad2/ to get it work.
Fortunately there are other ways to make this solution more generic. check it at http://www.vistax64.com/tutorials/244527-programs-replace-system-program-without-modifying-system-files-permissions.html
