Well, BS01 and the Wiki have nothing to say on this matter.
The movies did it almost certainly for clarity of emotion, as with the eye manipulations in the comics. It's a trick often used by artists and animators to show expression on a masked character, like Deadpool or Spider-Man.
My assumption is that they probably didn't, or at least not to the extent that they do in the movies. Considering most Kanohi were either carved or molded from solid Kanoka disks, I find unlikely they were able to move very much, if at all.
While the online sources say it was possible to make a mask in any shape regardless of power, this was hardly ever done, if at all, for the sake of being able to identify a mask's power on sight. So the easy answer to this question is neither because it would never happen.
If we're being hypothetical, I'd assume it would transform itself in line with its power. So the hypothetical answer, at least in my opinion, would be that it would transform into a Noble Pakari.