why ?
All unix based machines i.e. linux have localhost set as 127.0.0.1 and lots of applications use that information in the background.
If your machine is on a network, your own or the internet then it will have another IP address.
will show what network interfaces are available including local loopback bound to 127.0.0.1
if there is anything else there then you can run
to see how they are used.
if you have a private IP address 192.168.x.x or 10.x.x.x then you should be able to set the IP address
if your IP address is something else then it is being set by your network provider and you should speak to them.
If you want to spoof an IP address then remember that none of the packets from your target machine will ever get back to you.
let us know how you get on.