Q: Can I apply a pose to only some parts of the figure?

A: Yes, but it can be a rather tedious process. If an actor is locked (Object menu > Lock Actor), applying a pose won't affect that actor, even when the actor is subsequently unlocked, it will not have been affected by the pose. Obviously if you only want to apply the leg part of a pose, locking all the other actors of the figure is a lot of work. Too much work to contemplate in most cases.

There are utility poses for some figures that will lock/unlock predefined sets of actors. This can make the technique feasible. You can find such "Body Lock" poses for V4 and V3 in my Free Stuff here at Rosity. There are a set of Body Locks for the Antonia Polygon figure in the Poses section of the Antonia's Free Stuff site, they are included in the "APUtilityPoses1_2_0" package. Other authors may have published similar sets for other figures.