....what about the experience duration in this case? will it be 2 years for switching to an approved organisation?
You have to do the full Approved Course (ie 2400+ hours/2 years, Practical, OJT etc etc) to benefit from the 2-year work experience requirement.
All other forms of Module training, ie short courses, zero-to-hero, home study etc, is "unapproved", even when it is provided by an approved organisation. What counts then is the examinations, which must be run by an organisation with the approval to do so.
So, to be clear, you must complete a fully-approved course with a Paert 147-approved school with the appropriate Approval (Cat A, B1 etc) if yoiu want toi reduce the work experience requirement to 2 years.