Can I prepare my own deed of amendment/other legal documents?
In general, only lawyers are able to draw up legal documents (and do other "legal" work) for a fee, under the Legal Practice Acts of the various States and Territories. Therefore, only a lawyer can be paid to prepare such documents.
However, a person is entitled to draw up their own documents for their own use, but it is important to ensure that, when non-lawyers draft legal documents, the documents are still legally effective.
The fact that a legal document is not drafted by a lawyer does not make it "illegal" as such, although a non-lawyer who does so, for a fee, can be subject to prosecution (for example, S.21 of the Legal Practitioners Act 1981 (SA) states that a person who does something that only a lawyer should do, for a fee, can be fined $10,000).