This is a really frequently FAQ!
As far as I know, and from the many people who have emailed me both with this question and various answers, the consensus seems to be:
The new WA Police job codes that have a 4 as the first digit are just the same as the old 3xx job codes, but it's now a priority 4 job to put it a bit lower than priority 3 jobs to help organise jobs a bit better.
Got any more info? See you in the WA Police forums...