As the title, it would be helpful.
That should already be in there.
See menu Note > Split at Insertion Point
Select two notes and choose Note > Merge Note
There are also actions for split. Type \split
Aha, I found them. I used to search for items in the Help menu(cmd+shift+/), but these two actions are dynamic items in the menu, so I missed them. Perhaps they should always be present?
Split does seem to be there via Help. Of course, figuring out the verb is half the challenge.
Merge isn’t there, but I think that swaps out for Split, which is logical as an alternative. Not sure we need to have two separate items, with one always greyed out at any time.
We indeed decided to go for a dynamic single item not too cause unnecessarily long menus as (like Drew mentioned) they are mutually exclusive; it simply depends on your note selection (for merge you need to have two notes selected obviously) and split is only shown if the blinking cursor is in the middle of a note 
If the insertion point is at the start the same command is called “Precede by New Note” and if the insertion point is at the end of the note the command is called “Start a New Note”. The command itself always appears after the Duplicate command in the View menu, plus these options are also shown in the gear menu in the bottom right corner of the note.
See also these keyboard shortcuts:
| Shortcut | Command | |
|---|---|---|
| ⌘ / | Precede by New Note / Split Note / Start New Note | |
| ⌥⌘ / | Merge Notes |