Am about to purchase a very cheap xg, and while I get it ready to blue slip it I was thinking About removing the bench seat and chucking in a center console, just curious to what the rules are? Does this class as a extensive mod and required a engineers cert? Any advice would be great

I can't imagine it needing an engineers for that as it isn't structual. When I had my old HJ Holden panelvan I removed the benchseat and put Statesman bucket seats in it and it passed roadworthy no probs. All you can do I guess is put bucket seats in it along with a console but keep the benchseat just in case it doesn't pass then it's just a matter of putting the benchseat back in.
You could always get it passed then swap it to bucket seats... Should be easier that way I reckon mate.

I think if you change the bench to bucket seats, you do need to notify RTA. Something to do with registration of the vehicle as a 6 seater rather than a 5 seater...not sure if it's part of blue slip though.

Pretty difficult to turn a ute into a 5 seater.

Depends on the ute, but 3 seater as opposed to two seater would be similar.

I wouldn't expect any issues with swapping to buckets, tbh. But I live down in Vic so I'm not sure on your laws.