In the past you would have sent your ATPL to the CAA with your logbook containing your Mil Green Rating and in exchange for a small fee would have your licence revalidated for another 5 years.
Not quite.
The
old requirement for licence re-issue was:
A UK or JAR-FCL ATPL will be re-issued for a further period (5 or 10 years validity as appropriate to the licence held) if the applicant:
1. Holds a JAR-FCL Class 1 medical certificate valid for the first day of issue of the new licence.
2. Has held for any class or type rating included in the licence a Certificate of Revalidation the validity of which has not expired by more than 5 years; or
holds a current and valid non UK issued ICAO Annex 1 compliant pilot licence and is flying an aircraft type, using that licence, which is also included in the
applicant’s UK issued licence; or
is a Qualified Service Pilot in Her Majesty’s Armed Forces who is in current flying practice on a military type appropriate to the licence held (i.e. an
aeroplane for re-issue of an aeroplane pilot licence or a helicopter for re-issue of a helicopter pilot licence).
Now that Part-FCL licences are lifetime, there is no 're-issue' requirement for the licence itself once it has been converted to Part-FCL. Obviously, to use the licence privileges, you must hold a valid Type or Class Rating - and a valid IR or IR(R) if IFR privileges are to be exercised.