I'm not sure whether it's prorated or not sorry.

It affects your centrelink because you're getting paid in pre tax dollars (and ie getting the benefit of not paying tax on those dollars) and they need to "gross it up" for the purpose of determining your real income for centrelink purposes.

I'm not actually sure what the process is for notifying centrelink as I don't see that side of it, but they will need to know the full amount of your pay. Your group certificate/payment summary will show the grossed up fringe benefits