Yes, you can still do CASA Basics and SOE. But why? If you already have a trade qual (ie Cert IV), and have maintained currency, just get the Diploma. Shop around until you find someone you would like to deal with. After all there are only 4 ROs in Australia, it won't take long...
BTW, if you contact CASA, and want to do the CTC exam, they will tell you to see an RO, particularly if you're ex-ADF.
Feel free to PM me if you want more info, or if you disagree... fill your boots!