Export the modified V4 head as a morph, then load it to afresh copy of V4.

RENAME the morph into Custom_Morph.

The spelling must be EXACTLY like this:

Custom_Morph

 

Poser will now treat it as a morphbrush-made morph, and you can erase the parts of the morph you don't want with the "restore" brush.

Don't remove too much as you can't go back and forth as you'd normally do.

You might have to do a bit of blending to match the new features with the original faceshape.

Once you're finished, spawn a new morph so that you can use the morph brush and the Custom_Morph channel again in the usual way.