Is it possible to add child bones to a Rigify subrig?

Question

I'm new to Rigify, so maybe I'm not doing this the way it's supposed to be done. I had a look around but couldn't find an answer to what I was looking for.

Here's Rigify's limb.paw subrig:

As expected, the rig compiles when it is generated:

However, let's say I want add another bone to the end of the paw to control the toes:

The new bone is marked as a basic.pivot, but it looks like Rigify still assumes I want it to be part of the limb.paw and errors on it:

Is it possible to add child bones to Rigify's build-in subrigs?

(I realize there is a limbs.rear_paw that includes toes, but this is more about me trying to learn Rigify and wanting to know why this doesn't work.)

Answer 1

After generating the Rigify rig, you can add in edit mode any bone, child of an appropriate bone (could be thoose DEF deforming bones on 29th bone Layer, or ORG Original bones on layer 31 (counting from 00 to 31)).

Answer 2

Clear parent from your bone on metarig (Alt+P). Then in bone properties of your bone choose either basic.raw_copy or basic.super_copy rig type, then enable Relink constraint, after it in "Parent:" field you can enter name of the bone of generated rig (Foot.l for example or DEF-foot.l) you want your bone to be child. If you want basic.pivot you can create new bone and parent it to your bone and then choose rig type basic.pivot as usual.