I don't think we are.
You're saying they pass a MOT, I'm agreeing but warning you that doesn't make them road legal. You then say your MOT bloke says they are fine, I reiterate the same information and you tell me for a third time it's fine for a MOT
In terms of an MOT, we both agree that swapping the side lights, indicators and brake lamps from halogen/filament to LED will NOT cause a MOT failure.
However, having a MOT does not mean your vehicle is road legal or meets all required legislation.
You mention "sides/indicators and brake lights" "which do not provide a fixed and regulated beam of light" which is simply not true! ECE 148 has diagrams showing exactly how the light should be distributed for all of these functions, not just headlights, for ALL lamps. Just because it's not checked during an MOT, doesn't mean it doesn't matter.
Just for example, a indicator would need to achieve the following light pattern:
By changing the light source, you're invalidating the testing of that luminaire which means it's no longer compliant with the regulations and the type approval is voided, therefore it's not road legal. If you were to have an accident and someone claimed not to see you indicate or brake, using none approved light sources could add support to their claim even if it's not true.
In short, drop-in LED conversions are technically not road legal, regardless of light function or MOT checks, folk should be aware of that when making these changes