im trying to create a daz custom face morph. i have a custom face from another model i want to apply it on the genesis 8 fem model in blender. but i cant cut and past it straight away because i need to preserve original model vertices count otherwise it wont import into daz as morph. so im thinking perhaps there is a tool that molds an object in the shape of other object without changing the vertices or polygons count. i already extracted the custom face mesh. now all thats left is to mold the original genesis model face in its shape. something similar to how clay molds work in real life.
If I understand your question correctly,you are looking for the Shrinkwrap-Modifier. Add the modifier to the model you want to change and choose your "desired face" as the target. For further reading consult the manual.
However there is no way to get more detail than your polycount allows. That means the Shrinkwrap-Modifier might produce artifacts if the polygon-density of your model is far less than that of your target.
TheBeautifulOrc technically has the right answer. However, based on my personal experience, I would say that the shrinkwrap modifier, while very useful in some cases, could be problematic in your case. It may actually be easier to take the Genesis 8 model from Daz Studio, import it into Blender, take your custom model also, and import that into the same scene in Blender, and then use the custom model as as a visual reference only while you try to actually manually sculpt the changes in shape onto the Genesis 8 model directly. Depending on how much of a difference there is between the two to begin with, this may not actually be a lot of work. It may actually turn out to be very much MORE work trying to get the Genesis 8 model to take on the exact shape of the custom model instantly by relying on a shrinkwrap modifier. This is because, more than likely, the various parts of each face and head is just not going to line up, no matter what you do, leading to the possibility that one will end up crooked and smashed against the other in a terrible way that you just can't seem to fix. So this would be an alternative approach, IF you need it. :)