I have actorcore motions and I want to apply them to characters with masking, is it possible? to animate only body parts not the whole body

When you right mouse click on a clip, you have an option to remove what you wish to be masked.
Optionally you may sample the clip for selected parts (optimized) afterwards while selecting removed bones.
That would create 2 key-frames at the beginning and at the end of the clip.
If you delete those keyframes, you would end up with default T-pose for removed bones.
From that point on you may start animating removed body parts yourself or copy over motion from other sampled clip for those bones.