Hii Srini,
Yes it is possible to always pick up the Higher Priority of PDS. make the PV such a way that it can pick up any lot size and have a way ahead of future validity
Example: PDS A -priority 1- lot size from 0 to 999999999... and validity up to 31/12/9999.
PDS B - Priority 2- Should only be chosen manually., can be maintained constrained based,
Regards
Debahis