Outside of QSP accreditation, in current LASORs, what would a 747 pilot who TR'd 6 years ago have to do, if anything to begin a MPA TR course had he not remained 'current and valid'?
Assuming his last LPC/IR was six years ago, he would have to sit another LST/IR with a CAA Examiner observing the test. This is from the latest LASORs 2010 (which was only published in April 2011!).
The force is strong in Dan!
However, I believe the underlying concern in Cattivo's question is what would the 74 pilot need to do prior to beginning a further MPA TR course. Dan's answer is on the nail regarding what is required to renew the rating but there is still an argument that they can renew their IR during the TR course. Arranging a CAA Examiner to observe might be an admin issue for the course provider and so they might prefer you to start current as a bun, but that is different from what you are required to do.
In all my dealings with the CAA they have continually emphasised that Lasors is only a guide and that JAR-FCL is the provenance document and thus the law. It is also true to say that from Apr 12 EASA becomes the law and Lasors is being replaced by CAP804, a document still being complied, so there are many questions still to be answered.
It is an incredibly frustrating scenario for the individual, the employer, TRTO and dare I say it even the CAA.
In any doubt email licensing and get in writing the requirements based on your unique circumstances.