Not true I'm afraid. I think you're getting that confused with adding a microlight rating to an existing NPPL SSEA licence in which case the SEP/JAR exams you'll already have passed 'trump' the microlight ones.
It doesn't work the other way round. When converting from an NPPL Microlight licence to the NPPL SSEA the microlight exams are not counted as equivalent to the JAR ones and so you will have to do all of the latter. If you already have a FRTOL you won't need to do that again.
When I considered, going from nppl m to nppl sep, I phoned the BMAA who gave me the phone No of a committe member who drafted the nppl licence
I spoke to her, and was told, if I were a current nppl m licence holder, & wished to pursue nppl sep, further flight training in the region of 5 hours + sitting Principals of Flight again, not the microlight version, is all thats required