I think in function " head_script()" you can remove qa-ask.js value from $qa_content['script_rel'][] and add your new JS file with:
$this->output('<script src="' . QA_HTML_THEME_LAYER_URLTOROOT . 'my-ask.js" type="text/javascript">');
It will include "my-ask.js" file from your plugin directory.
Just redefine the functions in another Javascript file which is loaded after the Q2A core ones, and it will work fine. You can include your own Javascript function by using an advanced theme and overriding head_custom().
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