You can do a Requirements::block(...) to prevent a file from being loaded, then add your file - you'll have to copy whole file though.
Try blocking the script, then in setting up Requirements re-add script and then add your own script with a custom 'validationError' function which could change functionality. If you manually add them I believe it keeps the correct order, and they are 'global' functions so latest will override previous.
The current function appends a span with class "message required" to the parent element of the field with the "<field-name> is required" message. Instead change the function to change the field to, e.g. a red border (or the parent element).
You could do this with CSS selector on the span with "message required" :prev type selector (and set the span itself to display: none) but this probably doesn't work on many browsers.
You may need to block the default CSS and add your own/override styles where applicable too.
Thanks guys, I got it solved.
I had to do the block and then include my file as you guys mentioned.
However my JS file had to have the same content as the sapphire file and then I could override the function.
here is the code that worked:
What about the changes in the JS-File you did?