ok so this is the closest thread on the planet currently - Custom conformed metahuman inside of unreal engine 5.6 seems to work with the head mesh. OK great so now I want to do variations - Export the head > do so mods > use as morph target for custom variation
BUT simply exporting the FBX head or skm_face in unreal and reimporting EXACTLY the same fbx file as a morph target then it errors - Failed to import Morph target - Warning: FInterchangeMeshUtilities::ImportMorphTarget: Cannot import morph targets, the imported morph target geometry don’t match target skeletal mesh geometry topology. (LOD in 0)
so indeed yes - metahuman is currently BROKE for FBX export - interestingly enough I can import the .DNA file as a morph target - that works! wtf? the dna is exported from the creator when in assembly DCC export mode. but obviously I need to do something for the variations in a DCC but im using Houdini , not Maya or Blender 
AND. apparently in the metahuman SDK there is cmd tool called DNA2FBX …! this is the missing sauce no? WHY oh WHY is this sdk not available as a developer? apparently I have to beg for permission to access this? come on Epic