If you sign up for Romance Rewards now, you can do a Trading Places day at CSA from 10a-4p, which includes a shuttle ride. You should tip the shuttle guy a couple bucks.
And just a quick trivia item, 7-mile Beach (Long Bay) is only a little over 4 miles long. If you throw in the Bloody Bay portion, that adds just over 2 miles, but still falls short of 7 miles. The famous 7-mile beach in Grand Cayman is also well short of 7 miles long.
If you sign up for Romance Rewards, you can do a Trading Places day on Monday, Wednesday or Friday. You need to sign up at least 24 hours before you want to go, and I think you only get to do 1 Trading Places day during your stay. You will be taken to CSA by shuttle at 10am and brought back to CN at 4pm. If you want to come back earlier, you will have to pay for a taxi. You can click on the Romance Rewards link at the bottom of any page on this site and it will take your to the sign up page.
Check out the Romance Rewards. Once you sign up, you can use a day pass to travel to the other Couples resort in the same city. Since you're at CN, that would be CSA. I believe you leave earlier in the morning and come back by 4 pm. No swaps for dinner, but you'd be able to eat lunch over there and get a snack from Sea Grapes. They have the best sweet potato chips and dips! My mouth is watering now just thinking about them!! Yum!!!