Is there a possibility that, in addition to a rigify generated armature, I can place more bonews for a tail or something? I’d love to know how to do it in the easiest way possible: can I add it to do metarig, or do I have to add it to the generated armature if I want better results?
Yes. This video shows that.
Yes, you can add bones to rigify as well as interchange the original and pitchypoy sample rigs.
I use a custom metarig for most of my own projects that is a combination of the original Rigify torso, Pitchypoy arms, legs and face, plus many of my own control bones for various shapekeys, corrective controls or additional bones to help weightpaining.
Y4Lc1N linked a good tutorial.