Why is my home network a static IP*
How do you know it is truly Static from Comcast? Are you being billed for a Static IP? Generally, DHCP servers assign IP addresses to MAC ID's with a lease time for a duration. Rebooting doesn't necessarily get a new IP address if your MAC ID doesn't change. Does your router have a setting to change/spoof your MAC ID? You could use that to cause the WAN IP to change.
It is what is known as being *sticky* dynamic, meaning that it can change, but it is durable. It's normal.
If you have a router that has a MAC address cloning feature, you can clone a different MAC address in to it. This will force their DHCP server to assign a new / different public IP address to your connection. This is really the only sure way for an end user to change it.