What you might also want to look at it the Overall feedback setting in the Quiz activity. If you tick the option to display Overall feedback in the Review Options, you can then set messages to be displayed at different grade boundaries. As an example, under the 100% Feedback I would put something like:

<p style="color:#00aa00;"><strong>Congratulations, you have now completed this assessment successfully. The course will now be marked as complete.</strong></p>

and I would then add a new feedback field with a Grade boundary of the pass mark with the Feedback along the lines of:

<p style="color:#ff0000;"><strong>Unfortunately, you have not reached the required mark. Please attempt the assessment again using the button below.</strong></p>

If the pass mark is 100%, you will need to create an entry with a grade boundary of 99% (assuming it's not possible to get that grade without getting 100%) so you can display the "have not passed" version.