Hi heeped,
just to let you knw, whether you need to re-do all your subjects and flying depends on one person in CAAS. She's also the invigilator for all the ATPL exams conducted in Singapore.
As far as i knw, most experience flyers who are in the programme, with the exception of Massey graduates(only those with bridging course done, which is rare) have to go thru the entire course. Even for the fortunate few from Massey, they are required to go through the entire ATPL Exams again.
Well, you'll probably get tens of hours exemption, but put it this way, your chance in the interview(which is the biggest pain in the programme anyway) will increase...you'll probably have a smoother shot during your flying phase, but unfortunately, im incline to say that you'll most likely end up going through everything again.
Hope this helps.