I am reusing a rigged model I got from Blendswap. It is fully rigged (by rigify it seems) with the exception of the fingers. The rig comes with controls and shows no actual bones (which I judge would be easily extendable). It also has a complete armature ref bones that is already scaled to the model in a different layer. I took this armature's hand bones and skinned them to the model. The finger then seemed to work/pose ohk but the problem is that I cannot get them to follow when posing the model using the main rig controls (which yield weird deformation when posing the fingers after). I Googled and tried out what seemed to be solutions (like Child of bone constrains, Ctrl + J, ...) to no proper avail. Any assistance will be appreciated. Happy to provide more info that may be deemed needful toward offering the desired assistance.
I Googled further > found that I can select the main rig/metarig > go to Edit Mode > Go to Object Data > scroll to Rigify Buttons > Add two palms bones and the 10 fingers (by selecting each and clicking Add Sample) > scale them and link the joints respectively after. Doing this now and expect it will be all I needed. Just wished I could mirror and thus cut the work in half :)