I found an elegant and "non-hacking" method replacing Windows' notepad with notepad++. You don't need to replace the notepad.exe or assign x filetypes - it just adds one registry-entry and runs systemwide !
In the download package there're two files:
notepad_replacer.vbs (Notepad++ folder)
Copy the "notepad_replacer.vbs" to your Notepad++ folder.
Dim sCmd, x
sCmd = """" & LeftB(WScript.ScriptFullName, LenB(WScript.ScriptFullName) - LenB(WScript.ScriptName)) & "notepad++.exe" & """ """
For x = 1 To WScript.Arguments.Count - 1
sCmd = sCmd & WScript.Arguments(x) & " "
sCmd = sCmd & """"
CreateObject("WScript.Shell").Run sCmd, 1, True
In Notepad Replacer.reg change the path to the notepad_replacer.vbs to yours and import it (I use the portable version of Notepad++ and have included it into DO's scripts-folder).
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\notepad.exe]
"Debugger"="wscript.exe \"C:\\Users\\<YOUR NAME>\\AppData\\Roaming\\GPSoftware\\Directory Opus\\Scripts\\Notepad++\\Notepad_Replacer.vbs\""
For restoring to default notepad.exe just delete the above entry in regedit!
I never had any problems on different machines (daily use).
If you want an easy replacement without doing xx changes and also need it outside DO/Explorer and often open unknown/unregistered filetypes, there's no other way and IMO this is the best solution (all other solutions are either using an exe for replacing notepad.exe or modify xx reg-entries). You can see what it does and you can easily set it to default again by simply removing the reg-entry.
"Open with" is no solution (the same like with DO-viewer) - I don't want to assign each filetype I may open the way I want and the reg-templates simply doesn't work on all machines (and broke everything).
Be sure that I heavily test a solution before using it in a productive environment or offering here, I don't fight my sys.
An additional tip that's a bit out of the box: I have a Ctrl + Sh + E shortcut to open files in EditPad Pro -- you could do that for N++.
I use that shortcut to edit files with weird extensions (or no extensions!), as well as files that are normally opened by an IDE.
Similarly I have a shortcut to open things in Photoshop, instead of the default (the internal image viewer).