This seems pretty significant. And, I hate to sound gross but doesn't that technically mean a prosthesis could be attached as an extra instead of a replacement?
My takeaway: we have no idea whether the neurocontrol parts of the brain are this plastic. It might work great; it might totally fail. Nobody knows yet.
I would think about how to carry on common tasks with common items such as seating, sleeping, wearing clothes, etc. Perhaps 4 arms would be better than 3 given our symmetry but they're going to force the owner to use so many specially built stuff. I guess two are going to be optimal for a while.
Or attach the extra arms to a hexoscheleton and wear it only when needed.