Thank you for your reply.
Mass Products Changer is available in Store Manager for X-cart as well. In order to open it, you can select few products, right click and select Mass Products Changer http://screencast.com/t/8XlYLrSna
Also you can find some instructions here http://mass-product-changer-documentation.emagicone.com/
Please note: It is a separate addon for Store Manager and by default it works in demo mode and allows to change only few products at a time, so you could check how it works. In order to unlock all the functionality you'll need to purchase a separate license for this addon.
You can find more information here: http://www.xcart-manager.com/mass-product-changer
Feel free to contact us again if you need more assistance.