hi,
If you just modify the module's file; your changes will be displayed only when the page gets refreshed. But when a product is added to cart; the AJAX is triggered (by the vmprices.js -- the official Virtuemart Core JS file)..
The AJAX gets the variable from the flexible dropdown shopping cart plugin and print them inside the module.. So; the changes must be made via plugin's file first and then the vmprices.js file must be re-organized accordingly.
I can't give you step-by step instruction about this edit, because this is 100% custom modifications
(because you want to change how the elements work/look) and unfortunately we don't provide free support or step-by-step instructions for custom coding modifications.
You may purchase premium support:
www.flexiblewebdesign.com/premium-support
and let us take care this modification for you directly on your website though.
Regards.
Support