Set Animation priority

I'm planing to make a character who should be able to take a weapon up, plays the animation "GetArmed"(ClampForever) and ignores every other animation that would modify this animation.

For example the "GetArmed" animation is playing and the character is running. Normaly, he would swing his arms, but he should just play the Leg-part of the animation and ignore the arm part. Is that possible?

Yes. You need to set layers on your animation states - this will fix priorities. And set AddMixingTransform - it allows you to play animation on part of the body.