The reverse might be theoretically possible during activation (if you feed the QR code to your own custom device and your software implementation doesn't guard the keys, letting you copy those freely), but I suspect there is some form of attestation so it won't let you activate with anything but "trusted" devices (by network, not yourself). And if eSIM is already activated on a phone, you most likely won't be able to extract the keys, because those are most likely protected with some sort of secure element.