Hi Andrew,
It is possible to reshape an existing rig to match a different model, however it requires you to move and align a bunch of bones manually. This works (and I’ve done it a lot in my younger years), but it is very prone to human error and requires some problem solving skills to be able to complete that task.
That is where an auto rigging solution like Rigify comes into play.
You proportion the meta rig (template) to match the character and then generate it. The computer will then build all the components according to where you placed those bones.
I would still recommend some basic rigging knowledge before using rigify though as things don’t always go according to plan, and it is only able to build solutions for common setups (like characters). If you want to rig props or a character that is just a little bit different to ‘normal’, then using an Autorigger can actually be the long way of doing it.
