I was wondering if it’s possible to copy/paste bones between armatures, and if so, can they retain constraints/IKs/weights, provided they’re present on the new mesh? I want to be able to reuse bits and pieces of meshes and armatures without having to redo the same thing for what would be identical bones weighted to an identical mesh.
The short answer is ‘yes.’ In fact, once a rig is set up, adjusted, etc. you should be able to start a second file with a second character mesh and append the rig.
However, then you’ll have to adjust it to fit, rename the rig (if you plan to use the two characters together in the same production file down the road) and redo the weights. It works out to about the same amount of work as if you started from scratch with Rigify and is more error prone, so there’s not much of an advantage unless your two character meshes are identical… and if that’s the case, you’d be better off making a copy of the first rigged character in a new file and painting the differences (eye color, skin/surface/clothing colors, etc.).
I see. I ask because I just put a ton of copy rotation constraints on dozens of strands of hair on an armature, and I have another model of a different variant, but with that same hair and rig.