Thanks for your help.  But in this case, yes, I do know the email was legit, and it was triggered by someone trying to log into my account from an IP that was certainly not mine.  I will go back and try to discover what part of the world the IP was from, assuming it wasn't faked or multi-proxied.   The second email was also legit and was, as expected, from another browser session, and did indeed log me into my account (again).

I suspect that deciphering the specific language they used, which is still confusing, will have to be reposted to the proper forum by someone with enough stripes.  The reason for my posting was not so much that I needed to know, but that so Blockchain could improve their product.  Without someone informing them, I'm sure what the email said made perfect sense to them, but not me, and I suspect most users. 

The email did seem to indicate that I should be able to change my "wallet alias", which seems to be my "account login name", which very few sites will allow you to change.  So, I guess they are suggesting that if I'm concerned, I should create a new account and transfer balances to the new account?  It doesn't make any sense if that is so.  If that is the advice they intended, then say, "if ... you can create a new account, transfer your balances, and abandon your old account."

[[ .. For bitcoin44me: Of course the email was triggered by an "event", and is most often benign, or a phishing attempt.  However at times, these "events" are the only clues that any user has. Personally, I never want my users to ignore unexpected warnings, nor IMO, should you encourage silence from the uninformed.

And, yes, I've been a CEO and a CTO for 30 years now and have produced software used by millions, some of which might even be be running on your PC, and responsible for some very critical but invisible processes.  That said, I'm closer than ever to becoming a complete technology idiot, since I have yet to learn at the exponential growth rate of information.  If you know how I can accomplish this feat, please let me know.  ]]