Activating the Map:
You know how the map locks up after you beat the game, preventing you from traveling anywhere except your home and the Black Emporium? Well, I know how to make it so that you can travel!

First of all, you need to enable your console. Read on it here: http://www.gamefaqs.com/pc/988968-dragon-age-ii/cheats.

After that, press ~ and type: runscript zz_dae_debug. Then, select the options: World Map Debug -> Initialize World Map -> Act 3.

You should then be able to travel anywhere you want as before you beat the game. Now you ask, why would anyone want to do this? I'm not sure, honostly. I think it's nice to be able to travel where I need to for mods or for searching caves of Darkspawn.
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Known Issues:
The only issue that has been found is if you travel to the Gallows. Do not travel to the Gallows, otherwise you end up at the beginning of the mage crisis.
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Activating A Quest or Two (Optional):
To activate secondary quests you may have missed...do these simple steps. These steps do not require you to activate your map. I have tested most of these quests, and most do not work. Finding Nathalian worked for me, because I never finished the quest. If you've completed every single quest in the game, these steps will probably not work for you.

1. Type runscript zz_dae_debug in commands.
2. Click Plot Jump -> Secondary Plots -> One-Offs -> Work with a plot -> Finding Nathalian -> Set Plot flag -> Quest Accepted
Note: This is just an example for Finding Nathalian. You could go off from plot jump to find other quests.
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Good luck, remember to have a back-up save just in case, and have fun!
~Shasow