They are only required for the expressions because there are some unconventional morphs used in them, but you don't absolutely need them. Momiji is a fully original custom morph character. You can use the expressions without the head morph pack, but if ou try to inject the M_Xpress INJ you might get a hang in Poser since it will be looking for morph channels that aren't there. If you just inject the expressions that come with the V3 Base, and use the facial expression files; you'll get an error message, but you'll get most of the expression settings. They'll just look a little different because they won't have the oher morphs.