1. Your Mac address is the serial number of your computer for all practical purposes
2. Your IP address is almost NEVER a constant, even in your own home it CAN change.
The odds of an overseas ISP having the same IP address as a hobbyist, logging into TER, and being detected are small - larger if you are staying in the same hotel as the hobbyist, larger still if you are staying in that hotel for a long period of time (the IP's can recycle in as few as 24 hours).
However as someone who travels internationally extensively, I can tell you that first, TER is aware of "roving" members and doesn't give a crap. Second, I've yet to be blocked from TER as an "adult" site on any public wi-fi, from Singapore to Moscow to Malaysia to Argentina. Unless you're a hobbyist trying to post a review from a providers "legacy" IP address, TER isn't really going to care.
Lastly as to the "internal" Mac address - recognize the obvious. Different computers have different mac addresses. Use a $200 laptop when you roam and your regular pc at home.