It's possible to split a note from a script that's either stand-alone or in a plugin. See Help file > Automation, Scripts and Plugins > Scripting NoteCase Pro > Scriptable Program Commands > Application Commands > Nc_App_Action_Execute with the "tree_note_split" action name.
However, there's not much present ability to do much useful by using it, because there is no return of the note IDs for the newly created notes and because they are siblings of the original note that can't reliably be predicted. One could, I suppose, create a table of all existing notes before splitting a note and after, then process the two tables to determine which are new. But that's very cumbersome. I'd much prefer to persuade Miro to create a special API method to split a note that returns the note IDs of the newly created notes. (I'd like that method to include a parameter that can block the repetition of the new note title at the top of the note.)
If you want to create such a script, you might find some of the code useful in the attached script, Selected Laundry List to Notes.
Best regards,
Paul Merrell