Rated 4 out of 5 stars

For those who needs to transfer all notes produced by Message Notes to other
add-on with the same functionality. Applicable while e.g.: moving from TB 2.0 to 3.x.

The msgNotes.txt file is pretty simple - can be viewed/edited with any text editor.
This is the container where MN places all created notes.
Each entry in this file comprises 3 lines and corresponds to particular note:
1. Message-ID of the mail the note is assigned to
2. Note's text
3. Some magic number, possibly a check-sum

For transferring all your old notes created with MN you need the two first lines.
Why doing so I just ignored the magic number from msgNotes.txt item's 3rd line.
I am not sure if it is ok so.

Create a saved search folder in TB, saved search should cover all TB folders.
Saved search criteria should use the "Message-ID" mail header field >>>
use "customized" in saved search options dialog.
Search criteria should look as following "Message-ID includes <message id>".
Now proceed iteratively:
- Take a note from msgNotes.txt, copy the associated Message-ID into clipboard
- paste Message-ID from clipboard into saved searched options <message id>
- let's TB to find the mail
- use your new add-on for notes (MessageNotes replacement) to add the note
created previously for this mail using MN -- again copy&paste from msgNotes.txt
into mail text

Surely, it is possible to automate this process by a script or small sw.
I did all that manually because script development needs a good testing
before getting applied. I hadn't have a big number of notes to be transferred.