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Tails developers are working on MAC spoofing. If you care about this feature which might get used in Whonix some day. At least their thoughts on that topic are very valuable. You may be interested to join their Whonix unspecific development discussion:
[Tails-dev] [RFC] Design (and prototype) for MAC spoofing in Tails
https://mailman.boum.org/pipermail/tails-dev/2013-October/003835.html
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