Student Visa extension question

Curious if anyone may be able to answer questions about a student VISA extension. My present circumstances are I’m an Australian citizen, living in Brazil on a student VISA and working in Papua New Guinea. That last detail complicates matters some what.

Effectively I’ll be out of Brazil on work commitments when all the documents are ready to renew my student Visa and it’ll expire prior to my return. Preventing me from re-entering the country.

Would anybody know if someone with power of attorney can lodge paperwork on my behalf at the federal police in my absence? (A lawyer in São Paulo suggested the answer was yes but that was with the caveat of a sizeable upfront fee to perform in that capacity which made the advice seem questionable)

Can a student Visa be extended after it’s expiry date? If so is there a cut off period (for example, within 30 days of expiry)? Alternatively, can a new student Visa be issued based on a university course for which a Visa has previously been issued?

Does working in an alternate country violate any terms of a student Visa?

Finally, following expiry of the Visa, assuming no renewal, would 6 months be the period I’d have to wait before being allowed to re-enter the country?

If you’ve read this far and have come to the seemingly obvious answer of these questions should be addressed to the respective embassy, consulate, federal police or independent legal advisor. They have. All answers have been varied, confused or non-committal.

Any info would be appreciated.