116v

[-JKP-]

So... it is not unusual for a remedy or charm to be added at the end of a book. 

Not unusual at all. People often used blank spaces in books to note down births and deaths, or even, as you say, completely unrelated ideas notes. 
But not usually the scribes. 
If we start from the assumption that the writing is by one of the scribes -as suggested by the fluency of the Voynichese- then we reduce the possibilities of what it is likely to be. 
I still think it's two different notes. One is likely to be a curse of protection, the other could even be a colophon.

It's definitely different hands in the ones I've seen recently.

They are usually in a hand that is about 30 to 200 years later than the original document.