Is it possible to change the outcome of a beer in the fermentation stages? I am brewing a batch of Amber Ale right now and I was wondering if it would be possible to put something in with the wort while it is fermenting in order to change it's flavor. Could I add in like orange extract or something along those lines in order to get a citrus flavor in the beer? Is there anything I can do or should that have happened when I was boiling the wort in the first place? On a different note, would it be possible to raise the alcohol percentage of the beer/ make it stronger in this stage?
Could I add in like orange extract or something along those lines in order to get a citrus flavor in the beer?


Yes; search Google for "secondary fermentation additions".


  Is there anything I can do or should that have happened when I was boiling the wort in the first place?


There are flavor additions you can throw in the kettle but you'll get the most bang for your buck with (SANITIZED!) additions during fermentation. Don't think twice about an amber ale, though; wait until you have some more experience before improvising with recipes.


  would it be possible to raise the alcohol percentage of the beer/ make it stronger in this stage


Again, yes and no. In theory you can add more cane sugar, but in practice it only works with yeast that are highly alcohol tolerant. (Usually Belgian; highly alcohol tolerant yeast strains usually make no secret about their properties.) The yeast used for an amber ale is most likely not tolerant enough to go very far outside the recipe, and beer that is too alcoholic for the recipe generally tastes pretty bad.