[sgtnoodle]

At most you'll annoy your internet service provider. MAC addresses don't leave the immediate network they're used on, so you can do whatever you want within your home network.

[qwertay]

How would your ISP even know unless they are spying on data only available on your wifi network with an ISP provided router?

[Triv888]

I spoof my router's MAC address to change my external IP address at will. But yeah, hopefully they can't see the MAC addresses on your local network.