I finally figured out how to shapechange using the Petrified Orc Eye I had gathered - for other newbies who are stumped, you need an Unscathed Orc Bone Shard (maybe it works with others as well, dunno) in your inventory.
After shapechanging into an Orc, I thought I could blithely stroll into the Orc Mines on Zek - "hey, look guys, I'm one of you" - but no such luck! Got aggroed just as if I was still walking around as a Paladin!
So what's the use of the shapechange?
I did notice that there seemed to be fewer mobs in the mine tunnels, specifically I was able to get to the forges w/o all the Heroic Orc Blacksmiths I had encountered earlier - is that a result of the shapechange in some way? Not very intuitive for me here!