It is possible and the ATPL credits (as long as you passed all of them) will exempt you from the PPL theory training and exams. Get this verified though by your CAA (the one who will issue the license i.e. the authority that holds your initial medical file) so they will not be surprised when you sent them the skill test report for the PPL requesting the license.
Regarding any flight hours you have done so far, these will not be credited towards your PPL. You will need to do the full structured PPL practical training under one ATO. The flight hours you have logged during the integrated training program will count towards your total time of which you need 200 to pass the CPL skill test.
It is a smart thing to do as you will be able to pace your training in a modular course and time your completion with when the first signs of market recovery are starting to show.