Make program default editor for a file type
Shift-right-click on a file of a type; this forces the ‘open with’. Click ‘Choose program’, find it, and select the checkbox that tells windows to always open files of this type.
Change IE ‘view source’ program
has a default key that is the path to a program, e.g.
Add to context menu for all files
Run regedit. Create the key:
…if it doesn’t exist. Choose a name that doesn’t exist under it, e.g. Notepad2, and create that as key, and a key under it called ‘command’:
Make the default value under the first what you want to appear in the menu and the second what you want it to run, e.g.
“C:\Program Files\Notepad2\Notepad2.exe” “%1”