i know i can't really see what you were trying to say in the post, but i think i kinda understand and i'll take a stab at it...if this isn't what your trying to do then disregard my post..
so, personally i know when my connection was cable, that my internet only worked when i was using the NIC that my connection was setup with...cause on the ISP end they controlled it through the MAC address, so for example if i changed the NIC in my machine that would mean i would have to call the ISP and they would have to change that info for me to get a live connection...now with DSL that is not the case with me...
but to get to my point, if you know the MAC address of the NIC (or device for that matter, could be a router, etc...) that originally worked you can use the "hw ether" parameter with the ifconfig command to "change" the NICS mac address to be the one you specify with the command issued...i had to do that a couple of times and it worked fine...so if thats what your trying to do, then what i said above should work, as i know it did for me...the command would be something like the following:
ifconfig eth0 hw ether 00:00:00:00:00:01
where eth0 is assuming the device you are using, change accordingly if need be...and 00:00:00:00:00:01 is where you type the MAC address...