How about adding a new script tag to <head> with the script to (re)load? Something like below:
<script>
function load_js()
{
var head= document.getElementsByTagName('head')[0];
var script= document.createElement('script');
script.src="https://stackoverflow.com/questions/9642205/source_file.js";
head.appendChild(script);
}
load_js();
</script>
The main point is inserting a new script tag — you can remove the old one without consequence. You may need to add a timestamp to the query string if you have caching issues.