Answer:
A group can be changed to moderated if you submit a proposal (i.e. an RFD) with appropriate justification. After discussion takes place, if you wish to take it to a vote, a CFV will be issued just like for a new newsgroup.
If the vote passes (the usual criteria), then ausadmin will issue a control message which will change the group status to "m" for moderated.
Of course you will have to choose a moderator for the group.
The moderator should be somebody with plenty of time, who is reliable, quite familiar with USENET, and with flexible posting software so they will be able to repost approved submissions as the original sender without hassle.
Of course they should be interested in the newsgroup, and be able to act impartially (i.e. approve or reject submissions based on their relevance to the newsgroup, not on whether they agree with the moderator's own beliefs).