Adding Flavor to a bottled beer

In the glass it would surely work.

 

You won't be able to add it to the beer and re bottle it. You could, but I'd then wear gloves, and goggles, and all that stuff because they will probably explode.

You'll have carbonated beer already. Adding anything with nucleation points will cause it to foam up. Losing you carbonation.

Stiring in a bunch of stuff will oxidize it.

Adding fruit will add sugars, and nucleation points. You'll have a foamy mess, and then you'll have sugars that could ferment out in the bottle. Recarbing it, and probably overcarbing it.. Bottle bombs.

Your best bet, is to put whatever you want, in the glass and blend that way. You are a bit late to the party in adding things to a finished bottle of beer at this point. Try some out in the glass, note of what you added, how much you added, and formulate a recipe to incorporate what you added next time.

 

Not a good idea, for the reasons FATCITY gave. However, given your avatar, I think you should be able to go back and add your fruit to the fermenter.

 

You mentioned fruit or pumpkin flavor in your OP. There are flavor extracts you could add to your bottles and re-cap, but YMMV. Many people don't care for the artificial flavor of fruit extracts.