Is that 192.168.*.* or some other number in the second position? If it's 192.168.*.* then I would have to say that is impossible. Those addresses are not publically routable. If it's another number like 192.120.*.* then that is a valid routable internet address. However, if your "real" IP address is in the range of the non-routable addresses (192.168.*.*, 10.*.*.*, or 172.16.*.*) then yes, your entire network would be blocked if they blocked that one public address. If the real address matches the address seen on the remote end, then you could change your address and bypass their block (assuming they didn't block your entire network range).