Can I reconfigure AppleTV to allow access to my directv reciever?

No, the AppleTV does not work as a router. It's like an iPod for your television, that's all.

If you patchstick the aTV it can act as a regular system, but you would have to Google around to see if it can be set up to route between the wireless and wired interface. Even if it could, it wouldn't act as a firewall by default, so you would have to be very good about manually setting up firewall rules without any GUI.