The two on the front nine where added for variety primarily, as there was a run of similarly length two-shooters on the original routing.
Wille Fernie added his short hole "Ailsa" c.1909 (replacing a similarly named two-shooter), which was then shortened by James Braid ahead of the Open in 1923 (now known as "The Postage Stamp")
Braid also added two bunkers on the LHS "The Coffin" and one further forward at the foot of the bank, this stopped the bail-out to the left from where some balls were known to run back down onto the green.
He also lowered a bank at the rear of the green to open up the surface to wind and allowing balls to run through from the rear of the slightly extended green.
The genius of shortening the hole, encouraging a higher ball flight bringing the wind even more into play was evident yesterday, as was the deterent of "The Coffin" as not one player went into this on Day 1 from the tee.
Braid added the new 5th Hole "Greenan" along the coast at the same time.
I'm not convinced Braid did shorten the 8th. At that time some courses were measuring holes to the back of the green and I suspect the new yardage was simply a new measurement to the middle of the green. To me the big change that Braid made was putting in the bunkers at the bottom of the hill on the left.
The 5th was created when two of the earlier holes were joined together IIRC.
Niall
Hello Niall
Whether or not that measuring convention was in place in the early part of the 1900s or not, the following will hopefully convince even you (as the resident anti-Braid cheerleader on here

) that James Braid did shorten the hole in 1923.
The Dundee Evening Telegraph - on 8th June 1923 - extensively detailed the changes completed by James Braid:
“Nor is the course as long as formerly. Before the alterations its length was 6437 yards….To-day the length is 6415."
It then goes on to detail the changes and measurements hole-by-hole (on whatever convention used at the time).
For the
8th Hole "Ailsa" Bogie 3 the yardage prior to the changes was 127 yards, and after the changes 120 yards.Futhermore, as Braid is reported by Willie Fernie himself to have extended the rear of the green by removing a hump behind the green opening it up to the elements in his changes, the effective shortening may have been closer to 10 yards. Either way a club less, or perhaps two or more in a breeze, and consequently a higher ball-flight.
The assertion to Braid shortening the hole has been made in several other sources/articles relating to "The Postage Stamp" but I do not have time to repeat them all here, I'd like to get back to watching a great Open Championship unfold now...
Obviously if you have 1914-1922 Scorecard or other evidence that shows "Ailsa" at 120yds (i.e. prior to Braid's changes) I'd love to see it...I am very happy to let the truth dispell any story!
BTW - You are correct re, the 5th, this also was done...... by Braid.
Cheers!
Simon