Those two commands will allow traffic originated from one network(on eth0) to pass through the laptop to another network(on wlan0). They will not interfere with the normal operation of the laptop regardless of what interface is in use and how they got their IP addresses.
They will be effective only if both interfaces are connected to their respective networks and only if eth0 is getting gateway traffic ie, only if there is a computer/device on eth0 network with a gateway address equal to that of eth0.
If you dont want them to survive reboot, then the reason should be you do not want your laptop to act as a router without manually configuring it enhancing network security and not because they will interfere with normal usage of either interface on the laptop.
The set up will work even when eth0 gets its address from dhcp, you will just have to know the ip address given to the interface by the dhcp server and then set your xbox or any other computer/device default gateway address to that of the interface address and things will work just fine.