[O] org-crypt: Secure encrypted message against inadvertent change

[AW]

I'm using org-crypt. All text below a heading with the tag :crypt: becomes 
encrypted with saving the file and looks like this:

-----BEGIN PGP MESSAGE-----
Version: GnuPG v2

hQEOAxn9DjwjX2oYEAQAgLl/58dss1VVgmRb1rGIaNV2I5P+smcDjhWa5/arTMPE
9wjxHUpU/HSflCwnV5609H3J9ZSVubCpaUbV3Da0jnDUJuljFbSqapRym1PW0hFn
ApfLwze3HTj+A3eODf+p3kbDjFnII9Rfn7lWQ/6OmMrisQbvbsWzS3K/crgqu+cD
/j6m3nDURonKGStv5h7sgaSRuLGzqXvHXEnS+d1ad1ZomgTD4abZNvDYt9Y039FE
xYwRphWSBs+vtQ34resZewCa4s7h5SES5j839vQPWI4VyA4uRrfzYATHnHtoxfwA
RQWzUTeS16FFBxnjqqTXGXqH9go25Ovnl1Np9c2H7veH0lQB/hpwGbUJRnYCx5Nd
UlZ/U+aKQJl3aD+ulgOxJhTQNb9ToXxMpwS3FitsZHVh8OaRBLdgjRVFstWw3NhT
RTQ3Og0+ts34iKW+u+2ock/LqiDYFx4=
=+xma
-----END PGP MESSAGE-----

I really hope this example will not irritate your email software.

My notebook has one of those large touchpads and once in a while I hit it and 
go on with typing, but the cursor shifted to text somewhere else and I'm 
adding letters to a completely different paragraph, before I notice and 
correct it.

Well, this evening I added some letters inadvertently inside a PGP message, 
because the touchpad shifted to cursor to an encrypted paragraph. If I saved 
the file, the encrypted paragraph would have become un-decryptable (I tested 
this: decrypting no longer is possible).

Unfortunately I won't always realise what happened, e.g. if I don't watch 
while dictating into a speech recognition (Dragon Nat. Speak.).
 
And the encrypted parts are not needed often. So the destroyed PGP message 
might make it into my backups and if I try to encrypt it a year later...

Why isn't the text between 

-----BEGIN PGP MESSAGE-----

and

-----END PGP MESSAGE-----

read-only as a default ?

Really, an inadvertent change can destroy valuable information and it i