Hi Elisa
We are solving this problem by removing the "data-editorblocktype" tag from any blocks that you want to stop them from editing.
e.g.: This stops the user from editing it in the designer view:
<div class=""><p>Hello {{contact.firstname}},</p></div>
This allows them to edit the text / image:
<div data-editorblocktype="Text" class="">
If they have access to the HTML then they will be able to add it back in, so a combination of Abhinav's solution and this one may work?
Tim