On an analogous topic our insurer said they only required us to maintain our property to the standards that applied at the time of construction, but any replacements must comply with current standards. Our cover is for negligence. If an accident occurred and we were not found to be negligent then there is no claim. The accident might be tragic and unfortunate etc but not our fault and neither we nor the insurer has to pay for it. If we were found to be negligent then insurance covers it, but our next premium might be a bit higher!
Regardless of insurance, you still don’t want to be found negligent, so the question is whether the old rails really should be replaced. Is fixing or replacing ‘reasonably practicable’ IE not too hard to do and not so expensive as to be out of proportion to the risks. If it is reasonably practicable, I would replace the railings.
If the railings are close to compliance, say, in good condition, only slightly too low, not easy to climb, gaps only slightly too wide and compliant with the previous standard, then I would note that they present only a low risk, but plan to replace them in due course when you might otherwise have had to spend money on them anyway, say for repainting.