Sorry but all the routers I've used let me set the MAC address. No spoofing, just a setting.

Also you should power down the cable modem to let it pick up the new MAC address. Also, if such is not available then you call them and ask for the reset.

As to ICS, it's too much trouble for most. And support is rare because folk learned it was a tar pit. I don't see folk talk about it much.

If this is Windows 7 then Virtual Router might work then we configure your router as a WAP. (google virtual router and "router as a WAP').