I asked the CAA what I would need to do to add a CRI to my FI(R). Their response was:-
LASORS section H3.5 states 'an existing AFI (A) or FI (A) holder who does not wish to revalidate or renew that rating, but would like to gain the CRI (A) rating will be required to complete the following...' As you still wish to hold the FI (A) rating, you will be required to meet the initial CRI requirements as per LASORS H3.2. As you are the holder of an FI (A) you are credited the Teaching and Learning part of the CRI course. This information is detailed in H3.2.
Personally, I believe all FIs should be given a CRI automatically. This would then allow the FI(R) to train qualified pilots without the need for supervision.