After completing the stripping process of our figures and pulling apart the joints, we should have a Polaris figure in four parts (head, right arm, torso, and left leg) and Firestar, in three parts (head, body and left leg). At this point, it's fairly obvious that I can't match one Polaris arm with one Firestar arm, so I'll have to replace both arms to get the new Rouge figure.

Using a sharp Xacto knife, carefully trim the arms off the Firestar figure. I like to make as straight a cut as possible, rather than trimming to preserve a particular shape. I've found that it makes putting the pieces back together much easier.

Next, trim away the excess "joint material" on Polaris' right arm, leaving as smooth of a surface as possible. Try to approximate the same angle on the arm that you cut off the Firestar torso. Then, cut Polaris' left arm from the Polaris torso using the same technique.

At this point, we should have all of the pieces we need to assemble our new Rogue - head, torso with legs, and arms!