You seem to be getting excited by the term Honorary Rank. Let’s be clear the term Honorary has little real meaning, pretty much like a Kentucky Colonel, only that SCC Officers will be treated with the usual courtesy by Naval officers. After 1st April they may use SCC as their post nominal .
Regarding the use of RNR post nominals, it remains to be seen if they will continue using them. At the moment, they clarify their status as CFAV when writing by using LT(SCC) Nelson RNR.