FCL.930.CRI:
Conduct at least 10 hours of flight instruction in the role of CRI. If the applicant has privileges on both SE and ME the 10 hours shall be equally divided between SE and ME aeroplanes.
Each alternate revalidation shall be by AoC.
The FI requirement is for 50 hours so as long as you have done the 5 hours instructing in an MEP then you can revalidate. I believe that when you do an AoC in an SEP this can revalidate your ME/CRI privileges as long as the FIE includes questioning related to ME instructional techniques etc.
I'm unsure whether each alternate AoC shall be in an MEP?