You must hold a current ME class rating to hold an SP ME IR. This can be renewed at the same time as the SP ME IR. Whilst Part FCL exempts you from retraining for the SP IR if you have a current MP IR, there is no exemption for retraining for the ME class rating. How much you need must be decided and given by an ATO. To renew the SP ME IR by cross-crediting (Part FCL Appendix 8) you'll need to fly Section 6 with an examiner - EFATO, asym approach to go around, asym landing. If your SE class rating is current, you get SE IR privileges automatically by doing the ME test.