I actually have an alternative position that comes from my past work life job position. It wasn't the actual testing & tagging that was my issue, just the whole mountain of paperwork/documentation that health & safety requirements and work certification that is required to comply with mandates that it must be done. This is particularly so with a Company getting ISO certification so that they can carry out work for many other Companies these days. I was so glad to retire and not be buried in paperwork any more.
With Test & Tagging my understanding isn't that a tested item is safe for the following period, just that it was safe at the time of testing and provided the item is cared for then retesting is not required for "X" months depending on the particular work use it gets. It is then up to the persons using the item to regularly visually inspect it to determine if repair or replacement is required. As to your possibility of someone forging your Tag then if you have logged the particular item satisfactorily within your own records then you can do your best to protect yourself.
As to us as caravaners getting our own items Test & Tagged, I don't have any opposition to it and see it as a form of Insurance. I doubt that anyone here doesn't have their house, car and van covered by Insurance and part of that Insurance would most likely cover Public Liability. These days of litigation should have people worried about those last 2 words, Public Liability. If in the quite possibly unlikely event that someone were to be injured or killed by a faulty power cord or something else electrical that was your property and that you could have had for a reasonably small amount of money had Tested & Tagged, how would you defend yourself in Court? At least if you had had testing done then you could well argue that you had made reasonable attempts to ensure the offending item was safe, so long as you also regularly visually inspect for obvious damage. You could be on your own for any claim against you if your own Insurance Company decided that you had not taken reasonable steps to ensure the safety of any item that you own. I doubt that it could be argued to a Jury that you couldn't afford the price of Test & Tagging when they get told that you own a car and van with a combined value of many tens of thousands of Dollars.
For people who only use remote and free camp sites the risk of doing nothing would probably be minute but for those that use paid caravan sites it's inevitable that Test & Tagging requirements in some form or other will happen one day. Maybe the owners of those places will have to provide the power cords themselves, with a bond on them, and the power connection points will all have to be regularly tested. The people who make these rules don't care about the added costs that flow on to others. Regardless, Caravan Parks, whether privately or publically owned are someone else's workplace and I see the rules for current workplaces being eventually extended to them, whether we like it or not. Lawyers and Insurance Companies will make sure of it.
And that's my rant over.