Sorry, but my computer got stuck in English.
You are right in your explanation. What I am doing for the Karmeli alphabet is the following:

I use a font , called Avinor, in which I planted my special new letters at the first 255 positions, All in all I need 38 letters of which the five vowels with accent aigue already exist (for French and other languages.
To use my font I downloaded a free file, called Wxkbd20 and which you can find by using Google

I programmed it to bring out Alef by Control Alef on the Hebrew keyboard, etc.

It works fine and you can write Karmeli Hebrew very easily - if you know niqqud.

Michael Avinor