Qld BGR rules differ from the National rules.
Scroll down to STOPPER DOUBLE RIFLE page 7

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://ssaaqld.org.au/wp-content/uploads/2017/10/Qld-big-game-rifle-rulebook-2015-Edition.pdf

STOPPER DOUBLE RIFLE
a. Min. Calibre .400 – bore guns 12 bore minimum
b. Min. bullet weight 400 grains
c. Min. muzzle energy 3500 ft lb
d. Scope Penalty - refer Section
6 - Sights
e. Centre-fire double rifles only
FIRING SEQUENCE Stopper Double Rifle (12 shots on 50m Slow Fire Pistol Target)
50 metres/yards - 1 target only
- 4 shots offhand, 2 from each barrel (30 seconds) 25 metres/yards - 2 targets 2m apart - 2 x 2 shots - 1 shot at each target off hand (per bracket of 2 shots) (10 seconds)
- 2 shots off hand -1 on each target left hand first (7 seconds)
- 2 shots off hand - 1 on each target right hand first (7 seconds)

this is most probable where it is 'official' for our QLD postal shoots.
The National rules however differ!
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.ssaa.org.au/wp-content/uploads/2021/02/BGR-National-Rules-No.4-2016.pdf

To summarise
Page 6 - 3.2 - Group 2 specifications
Page 7 - 3.6 - Stopper double requirements
page 8 - 4.4 - Double Rifle firing sequence: (A competitor using a double rifle must fire the barrels in sequence. This means that in any firing sequence no two consecutive shots can be from the same barrel.)
Page 13 - 5.75 - Stopper double number of shots & distances

So no deliberate change in barrel firing order is required, only that BOTH barrels must be fired, the sequence is inconsequential!

Humble apologises to all if I've waffled on (a lot)!
I just hope it makes sense!