My view of that is that it applies to ring finals supplying accessories to BS 1363.
In this case the ring final is not doing (only) that, therefore 433.1.204 does not apply - you may not use it.
So I will ask you again - where do the regulations say that a ring final does not have to satisfy Iz ≥ In. There must be somewhere, other than 433.1.204, becasue 433.1.204 clearly does not apply, and yet you keep claiming that using a ring final to supply a CU does comply, so you must know where that compliance is created.
In this case the ring final is not doing (only) that, therefore 433.1.204 does not apply - you may not use it.
So I will ask you again - where do the regulations say that a ring final does not have to satisfy Iz ≥ In. There must be somewhere, other than 433.1.204, becasue 433.1.204 clearly does not apply, and yet you keep claiming that using a ring final to supply a CU does comply, so you must know where that compliance is created.