It is pretty pointless, but my plugin can get you started.
Generate the metarig and use it to rig your character.
once ready you can transfer the automated weightpaint to the unreal bones.
In fact, you can unparent the mesh, parent it back to the ue4 rig, and make sure that the weight paint works still.
You’ll have a bunch of trash data from the auto paint you can dispose of. Best way is to manually lock all of the vertex groups matching the epic skeleton and deleting all non locked vertex groups.
Assuming you have it completely finished and weight painted correctly you can export a regular FBX, import in unreal and just select the default skeleton instead of leaving g it blank (which creates a new one).
this way technically you can just change the mesh on your character and do not need to re-target…