The best way to remove these particular bolts (on the arch) would be using a scaffold platform. And it would probably end up being a lot cheaper (compared to fully insured rope access workers).
Damage to the site using a scaffold setup would only be temporary.
Other areas that can be more easily accessed via abseil should be done by an industrial rope access company. They might cost around $2-3k?? for a couple of climbs that can be removed in a day (long day including travel time). And this wouldn't include any kind of patch work.
Any official shortcuts should be investigated by WorkCover in my opinion as I don't believe amateur bolters should be encouraged to carry out this 'work' and the risks go far beyond those accepted by typical Track or Bush care volunteers. It might be a good time for NPWS to begin setting up a framework to handle these issues sensibly and within safe work practices.
Further to this, since the arch's structural stability has been called into question it would be very inappropriate to expect work to be done to the underside of the arch if they have some advice that suggests it is unstable?
As a disclaimer; I am a rope access diagnostics engineer and am looking at this predominantly from a liability point of view.