Hi,
It depends what you want to do exactly.
You can use a product custom field (using HikaShop essential or business) or you can implement a special algorithm which will determine the image to display depending the product stock.
But in both cases, even if it could require some little view override ; there is no heavy programming required.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.