Hmm , much confusion
There is no connection between RYA exams and the requirements for MCA coded yachts. You can quite happily do the exam on your own boat , in fact the RYA prefer it.
If you are engaging a school
, and they provide a boat AND that boat is UK flagged then it must be MCA coded.
So there is no reason not to use your own boat , or in fact to do the exams on one of your friends boats and you can all crew for each other, in fact the examiner may do more then one YM exam at a time.
If there is a few of you it might be cheaper to fly the examiner from the UK.
Have you definitely confirmed the school
itself isn't flying out the examiner. Note the school has nothing to do with the examiner, you apply to the RYA