See my post on the NPP forum: https://community.notepad-plus-plus.org/post/103383. It takes the ideas presented here about creating a user-defined language and adds a Python script to be able to toggle line breaks by replacing '~' or '~\n' with '\r\n' and back to '~'. The script can be tied to a keyboard shortcut for easy access.

Thanks to phaxmohdem, chris-k, and kedar-ghadge for the UDL starting points!