Suggestions? Pick one:

• Fly your itin as booked.
• Cough up the miles & change it.

This caught me last year when I wanted to change my CVG DO round trip to a multi-city so I could work in a visit to my mother on the way home. We ended up making a separate trip.

You have to read the terms on the cert. They mean it. It's not the sort of thing I would make an issue of.

You can always make your concerns heard through Talk-to-Us, but as NW merges into DL (and WP Visa likely is replaced by Amex) I wouldn't expect any changes.