I came across a large market hall constructed in approximately 2008 which has fire exit sliding doors linked into FA system that open on actuation. No EDR (typically green coloured box). Red manual call points installed adjacent to doors. As most of us will know, the sliding doors should have been provided with a manual EDR as well. Q1 - can BS 7273 Pt4 2015 be applied retrospectively, see RRO Pt3 (d)?   Q2 - can any justification be made as to not fitting EDRs?

There is no statutory bar unlike with the old Fire Precautions Act - if the risk requires modernisation of precautions so adequately control it so be it (conversely if the old standard of precautions can be demonstrated to still give tolerable protection then it needn't automatically be modernised).

British Standards are not law, in theory (& practice) you can deviate but you fully accept the onus for demonstrating why it doesn't compromise safety.