We were able to do such things in Smalltalk as well. The Parcel format was designed to freeze the VM, apply a code change atomically after morphing any objects

We were able to do such things in Smalltalk as well. The Parcel format was designed to freeze the VM, apply a code change atomically after morphing any objects which were changed, then complete any in-flight transactions with the new code. Once, I logged into a running Web App Server image and manually manipulated DB lock in the ORM, because we had to do a demo before we could fix a particular DB bug. (So I was doing this "live" during the demo. Mind you, this was back in 2002 or so.) We could also use the image saving feature to basically create a "live" core dump while letting the server continue to recover and run.