I think you may be talking about the MAC address in the actual hardware, not the assigned IP address. If I’m not mistaken, even those numbers can be spoofed/masqueraded also.
You can spoof MAC addresses very easily (IPs are a snap to mask as well) - it’s a standard feature on many routers. A few of my home networks are cloned to match one single MAC address.
I do it because my cable internet won’t work if I reboot all and they start up out of sequence - the router and service marries to one single MAC. To reset it all takes 5-10 minutes of being powered down.