Can I still cook a prime rib that is two days past use by date

See https://food52.com/hotline/45533-is-chicken-with-a-sell-by-date-of-2-days-ago-that-has-been-in-a-refrigerator-that-promises-me-it-is-3 for a comparison discussion. You'll like it!

yes, it should be fine. in the future,store it in the bottom rear of your frig- that's the coldest spot- and it greatly increases the shelf life of perishables.

Most likely, yes. Just give it the ol' smell test. You'll know if you cant. Merry Christmas and happy roasting.