On Mayflower Road (after the 28 miles on route 58), bear right to stay on Mayflower Road (not, as previously, left onto Colchester Street). Follow the arrows onto Brook Street, Spring Street, and High Street, and rejoin the previous route on route 80.
This is, by far, the most significant change. We are avoiding the 8 mile stretch of route 6A through Barnstable and Yarmouth. Instead, we take a visit to Hyannis, and then we ride the entire length of the Cape Cod Rail Trail.
On the Service Road, do not, as previously, turn left onto Oak Street. Instead, continue straight, and merge onto (the charmingly-named) Shootflying Hill Road. Warning: Be sure to stop at the stop sign at the merge, because traffic, merging from the right or oncoming, does not stop.
Just after the stop sign, on the left (on "Patti Page Way," no less), is a porta-potty (and possibly also indoor toilets) at the Cape Cod Chamber of Commerce, conveniently about halfway between checkpoints 2 and 3.
At the end of Shootflying Hill Road, turn right to take route 132 (the unpronounceable "Iyannough Road") and Bearses Way into Hyannis. On route 132, you have the choice of riding on the shoulder, or on the bike path. If you take the bike path, watch for traffic at driveways. When you reach Bearses Way, the right turn lane is very narrow, so you may prefer to take the bike path, starting at the Cape Codder motel (which, incidentally, is planning to rebrand as "Margaritaville Resort Cape Cod").
From Hyannis towards Yarmouth take (unsurprisingly:) Yarmouth Road, which is dangerously narrow for just over a mile, and must be ridden single-file. Most of Yarmouth Road can be bypassed by bearing right onto Old Yarmouth Road, which runs more or less parallel, gets renamed to Rosary Lane, and then rejoins Yarmouth Road near the end of the dangerous/narrow section.
In Yarmouth, you pick up a narrow bike path, which is not the Cape Cod Rail Trail (but leads to it). Be considerate of pedestrians, and watch your speed on a steep left curve after the golf course. Also, there are two intersections where you have to virtually come to a stop to get between the barriers. The second set of barriers is at the entrance to the town dump, so be cautious with the motorists.
After the dump, you reach Peter Homer Park, which is the start of the Cape Cod Rail Trail and the location of our new checkpoint 3. Also, this location has flush toilets.
From checkpoint 3 to checkpoint 4, you just take the Cape Cod Rail Trail. It even has its own rotary, just for cyclists. Be sure to follow the arrow towards Brewster.
On route 6, do not, as previously, turn right onto South Highland Road. Instead, stay on route 6 for another mile (1.6 km), and take the Highland Road exit. Rejoin the previous route by turning left onto Highland Road.
When you reach Provincetown, bear left on Commercial Street (not, as previously, right on Bradford Street), and the new finish line is just a half mile (0.8 km) on the right, at the Surfside Hotel.