Ok. the appointment debate seems to have taken over the handling of the spectator/coach issue.
@RustyRef That may be so where you referee. But it is not the case in the particular circumstances I was in. Once appointed through the process mentioned, i am a match official the same as if I was appointed in prior by our 'appointments team'.
Here is how the process works in summary:
During the premiership season appointments can only by done by the appointments team. Any last minute changes or midway replacements (injury etc) can only be done with the approval of one of appointments committee members by phone, verbally or text.
The finals series starts after the premiership season and all games are sudden death. Due to its nature these games can get very heated. There are much fewer games in the finals series and played on only a few grounds with multiple fields. There are generally 4 game on each field in 4 time slots starting with the more junior/lower division games. All games are appointed a referee and 2 NARs and if known to be a 'problem game' a 4th. Some games can be appointed a 4th on the day if seen to be needed (like the one in OP). Some very late appointment changes can happen on the day due to necessity (eg, an AR calls in sick with short notice).
All officials who have games on the ground are encouraged to get there early and stay back after their game not only to support their colleagues but fill in if the need arises (obviously the are considerations on how many games can an official do).
Each ground is designated one or two 'Senior Officials' by the RA management committee. They are senior experienced referees who know the capability and ranking of all of our members and usually hold position within the management committee or the appointments team. They get to the ground before the first game and stay until the end of the last game (sometimes appointed to referee in one of the senior game). These Senior Officials have the list of all appointments on the ground and are given authority to make late appointment changes (but only when necessary).
This has been practiced in our district for many years and has never created any issues but certainly has solved many.