A few important things to check when you are making animations:

1) Make sure that you have the 'auto key' set, or else you have to set each key individually

2) Make sure you are changing the pose in EVERY frame that makes up the animation. IF you re-site the bone position in frame 5, say, the thing will jump back into the old position in frame 6 unless you change that one too.

You can change ALL of the animations, but for the crossbow aim and shoot animations, they are in the BI/data/animations folder, so make sure you are changing the right thing!!!