it’s possible.
you can start separate, take what ever you need from rigify (neck-head-face for example) and generate the rig.
making your own rig for the mechanical parts (a different armature object) after that join the two armature to one object (Ctrl+j). after that in edit mode you parent what every needs to be parented from both previously separated rig to each other.
i used this technique here where i created the limbs bones from scratch for the mechanical limbs parts. and used rigify for the organic parts (sorry didn’t record the rigging cause i was exactly trying to learn this by trail and error):
also if you you think you want some limbs from rigify but you don’t want to be a deform bone and just parent to bone. you can unchek the “Deform” for those bone in the edit/pose mode of rigify MetaRig before generating the rig:
