One possibility is the car will alert us slightly before it changes lanes so we can do a quick confirmation check before it actually does it. if we don't want it to we simply hold the steering wheel preventing it from moving over. But, I can see that leading to trusting it while not going through the normal checks.
IMO, to be safe it would need to get explicit acknowledgement from the driver to proceed, like a tap of the stalk or something. Boy would that be annoying. In heavier traffic it would usually mean missing the opportunity. It would be, essentially, completely useless as L2 -- basically it's like a navigation aid at that point prompting you to change lanes. This will only be useful if it's L3 and can truly do it unsupervised. And it looks like EAP is not going to be L3, and yet they promised supervised lane change, so.... ???
Maybe Elon can clarify what they intend EAP -- this product we have already bought and paid for -- to actually do with one of his always-elucidating tweets.