I finally got round to activating my Diners card. The phone agent was very helpful and offered to check which ATMs near me can be used to change the PIN: two discount stores and a petrol station. Very upmarket!
I also received in my M&M inbox a Lufthansa Business Lounge voucher which is part of
the sign-up gift. I was going to gift it to someone in the US so they can use it to visit the business lounge in IAD, BOS, etc. when flying domestic but it turned out you have to be departing on a LH Group carrier. Also according to the small print the Voucher is "valid for the primary Miles & More credit card holder or a travel companion" which makes it less useful as I'll need two guests. It goes on to state: "The sale as well as the offer for auction of the lounge voucher to a third party is prohibited." Presumably it's ok to give it away but do I really have to be present for someone to use the voucher?