The UK and EASA require 'differences training' when moving to a different twin-engine aeroplane or to a single-engine piston aeroplane fitted with a number of different systems such as: VP prop; turbo-charging; retractable gear; single-lever power control (FADEC).
Differences training requires training in the aeroplane or a suitable training device delivered by an appropriately qualified instructor. There is no official syllabus and so it's down to the instructor, or the club/school they're working for to decide what is necessary. For a VP prop I'd expect a few hours groundschool and a flight or 2. The instructor then signs-off the difference in the pilot's logbook. For single-engine piston aeroplanes, differences training is valid indefinitely, otherwise it's valid for 2 years from the last time you flew that type.