I know that you can't do accg340 unless you passed either of the units but my friend got PC and he applied for a waiver to ACCG340 and his waiver was granted.
If you are doing accounting then it's ok for you to get pc for accg253 but if ur doing applied finance, I think you either have to redo the unit or apply for a waiver to do the subject which requires you to pass the unit (eg. ACCG353,ACCG350,ACCG329).