I would never trust a guy at a tire store to redesign my tires. If you need more snow traction just but a set of snow tires. Cutting sipes into a tire will break up the tread blocks and make them chunk in cornering. They are 3 things that make a tire work in the snow. Tread depth. tread design and rubber compound. Without one of them the traction is dimninished.
I would say save your money.

 

Cool, that's what I did. We've had ice and snow all week and the tires are doing just fine.

Thanks for the input everyone.

Dave

 

Jim nailed it. If you think that the tires you've chosen need to have the siping service done in order to suit your needs, then choose different tires.