You right click "Empire: Total War" and "View Downloadable Content".Yeah you can definately do it anytime.
Okay well having looked in the custom battle section I can confirm that my Special Reinforcements and my Amazon units are available after activating their codes. They just don't show on any "DLC" tab like the FAQ says they should. Odd but hey, they're there.
Haven't got a code from Amazon UK yet >.<
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