Turns out you won't be able to sell/trade your e-mailed codes since it asks you to sign in with your e-mail and it automatically redeems the code for you.

Proof here: (Taken from Se7enSins)
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Below you can see the countries involved; as you can see the UK isn't.

To receive early access to Specializations, you must purchase Halo 4 Standard Edition and play the game while connected to Xbox LIVE by 11:59:59 P.M. Eastern Time on November 20, 2012. A download code will be sent to the email address associated with your Xbox LIVE account by November 30, 2012; any email returned as nondeliverable will not be re-sent. Limit: one code per gamertag. Xbox LIVE Gold membership required for Halo Infinity Multiplayer (sold separately). Offer available to users 17 years of age and older in the following Xbox LIVE countries: United States, Canada, Chile, Mexico, Colombia, Brazil, Japan, Hong Kong, Singapore, Korea, Taiwan, Australia, New Zealand, and India. Offer is nontransferable, not redeemable for cash, and cannot be combined with any other rebate or offer. In New Zealand, only adult accounts (18 years of age and older) can download or stream content over Xbox LIVE Marketplace. Taxes, if any, are the sole responsibility of the recipient. Download charges may apply as set by your ISP. For Xbox LIVE Terms of Use and system requirements, see [ Register or Signin to view external links. ] . Offer provided by: Microsoft Corporation, One Microsoft Way, Redmond, WA 98052.