My understanding of the regulations is that the exclusion relating to the regulator and flexible hose on older caravans relates only to those, as in effect the owner is not breaking any gas union when replacing them, if you disregard the jubilee cilps on the hose to rigid pipework.
With bulkhead mounted regulators the union between pipe and regulator has to be broken, and as they have cutting rings to make the gastight seal, they have to be fitted precisely, or they are liable to leak.
The question relating to sliding a fridge out to effect an element change, without breaking the gas union , any movement of the pipework can cause leakage, so the unions should be leak tested after the fridge has been relocated, and using washing up liquid is not permissable , as the salt content degrades the pipework over time!!! and it is easily detectable if things go wrong.