The updates that have been released for FM13 DO WORK for FM12.
How to update your game:
1-Download LFCMarshall's Summer 2012, Starter, and January Updates.
2-Extract the Summer update to C:\Users\USER\Documents\Sports Interactive\Football Manager 2012\Editor Data (if you do not have a folder named "Editor data" then simply create one)
3-Repeat the previous step for both the Starter and the January Updates. If you get a message saying that a certain file exists and is about to be overwritten just click yes to all
4-You have to start a new game in order for the updates to take effect.