It would be nice if Twistpad could replace Notepad - since lots of file context menu items are already pre-associated to notepad.exe in the Registry (for example, the "Edit" action of .LOG files, or .INI files).

This could be done via the "Debugger" entry in "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\notepad.exe" as follows:
http://stackoverflow.com/questions/2984846/set-image-file-execution-op tions-will-always-open-the-named-exe-file-as-defaul

Twistpad.exe would need to accept an additional flag such as -ignorenotepadexe - because doing this would invoke "twistpad.exe notepad.exe %1".

This is how the notepad replacement feature works in both Textpad and Notepad2:
http://www.flos-freeware.ch/doc/notepad2-Replacement.html