Adding a USB entry

How do you add a USB entry? Specifically, a device that is similar to existing devices except for a different product code. I see the list in /lib/modules/.../modules.usbmap which seems to be a reflection of /etc/hotplug/usb.usermap or maybe /etc or maybe I should add to /etc/hotplug/usb.handmap The documentation for this area seems rather sparse on the web. Paul Alfille