PHP amending for Virtuemart 1.1.9 / Joomla 1.5

Project is to provide code to amend existing Virtuemart files so that new products and emended products do not re-order to position 1 within a category. Currently all new products and any amended products is given position 1 in the default ordering. Our aim is to keep the existing ordering so our best sellers are in the top 100 all time, but every time we change a product or add a new one, it jumps to the top position. We want the code supplied to us to we can amend again if a future update over writes the hack.