Just reading the latest BASC Magazine. In the Northern Ireland section it looks as if the PSNI has agreed to a format for licensing whereby rifles are put into various classes according to size / usage etc. And if you want to change a rifle you can simply take it to a RFD and exchange for something else in the same class. So if you want to change say a 308 for a 7mm-08 or a 270 it should be simple. You will be licensed to hold a rifle / rifles of each class etc.
Just maybe some sense is being seen at last, and the rest of the UK will follow suit, but not holding my breath.