You have completed the first year of the demo, and want to continue your current game (after having bought BoA that is...).
This is possible with just a small file manipulation.
1. Install the full game over the demo.
2. Patch it, you must be in 1.08.
3. go to the save folder (which is left untouched by the install), named BoA\saves, open the campaign75 folder.
4. Zip the 1775 Campaign.hst file and send it to [email="email@example.com"]firstname.lastname@example.org[/email].
5. Within 2 days you will receive the corrected file. Put it and overwrite your old one.
Some notes on the demo, in case you wonder...
The Demo can't be unlocked just by modifying the data and scenarios files.
The Demo won't also be able to play correctly the others scenarios, even if found by some others means (a friend or on a P2P network...).
The Campaigns are particularly locked in this regard and there is no means to circumvent the Demo limitations.
Hofstadter's Law: "It always takes longer than you expect, even when you take into account Hofstadter's law."