I assume Hexagon is the best freebie for doing this kind of work
For quick and dirty work:
Send Genesis to Hexagon. Keep Genesis in DAZ Studio 4.5, which is running at the background while you diddle with Genesis in Hexagon.
Do what you planned to do to Genesis in Hexagon. Send it back to DAZ Studio, where you had that raw, unmorphed Genesis waiting. Make sure that both the figure you’re sending is at base resolution (no smoothing, no high res) and ditto for your Genesis.
DAZ Studio asks you “Create Morph?” when you switch there. Name the morph, place it under right category (like, if it is head morph, look for head morphs and tuck it under, say, sci-fi/fantasy).
Yank the knob to your new morph the max, go to Joint Editor if you drastically changed the shape. Adjust rigging (right-click) to shape, memorize figure shape and rigging (in figure menu).
Yank the knob down to 0.
Go to file menu, save a morph, pick the morph you just created, save and Bob’s your uncle.
This should work out OK for “for my personal library” solutions. I’m pretty sure that for “share with others” there needs to be more steps…