Yes, it applies to tests taken outside the UK - it applies to any test where the competent authority of the applicant is different to the one that issued the examiner's certificate.
There is no periodicity stated for the briefing - the law states that the examiner shall not conduct the test unless he has informed competent authority of his intention and has receive a briefing. On the one hand, one might consider that once a briefing has been received, that part of the requirement has been met for all future cases; on the other hand, it might be interpreted as requiring a separate briefing for each occasion. How the UK CAA will interpret the requirement remains to be seen.