Im an animator, not a programmer, but maybe You could make a 1D blend space controlled by time. You would have to make a timer or Time function of sorts, but this would allow a seamless blend between the poses, and would allow it to be interrupted, since its contained in one state. You could also go deeper and make a 2D blendspace controlled by time, and another variable that becomes a certain number like 1, 2, or 3 depending on what attack you want to be played. that way you could have many different attacks all in one blendspace.