I often know who's on my site at a given moment (for example, they're on the phone and I direct them to a web page) but do not have their email yet. I'd need to name that visitor for spotting later but although the system assigns them a numeric name to their IP (e.g., 983567) with no other data needed, I cannot change that name to the real one.

Why would the email be required in such case? It wasn't there to start with... Can it be made optional in that form, please? Later, if I get their email, it could be added by associating with the same IP. This would add so much insight!