Alright, I did it with a jquery workaround.
I added a page for user options, where users can change stuff ... which is made with jquery and setting cookies.
By the way, I am heavily using jquery to add features to my q2a installation...
You would use this jquery line to uncheck all checkboxes for notifications at once:
$("input[name*='notify']").attr('checked',false);
Hope that helps!
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But of course, this is not a consistent solution. Better would be an option within the user database & php.
$("input[name*='notify']").attr('checked',false);
$("input[name*='notify']").attr('checked',false);$("input[name*='notify']").attr('checked',false);
$("input[name*='notify']").attr('checked',false);