Yes, you surely can avail the NCB if you change your insurance provider at the time of renewing the policy. All you would need to do is producing a proof of the earned NCB from your current insurance provider. You can produce the original copy of your expiring policy and a certification that you haven’t filed any claim for the (expiring) insurance plan. A renewal notice or a letter stating that you’re entitled to the NCB from your previous insurance provider can be a proof for this.
In South Australia, since July 2016, CTP is no longer provided by the Motor Accident Commission.The government has now licensed four private insurers - AAMI, Allianz, QBE and SGIC, to offer CTP insurance SA. The scheme allocates one provider for 3 years as part of vehicle registration. After July 2019, vehicle owners can choose a different CTP insurer and new insurers may also enter the market. 
The minimum coverage defined by German law for car liability insurance / third party personal insurance is €7,500,000 for bodily injury (damage to people), €500,000 euro for property damage and €50,000 for financial/fortune loss which is in no direct or indirect coherence with bodily injury or property damage. Insurance companies usually offer all-in/combined single limit insurances of €50,000,000 or €100,000,000 (about €141,000,000) for bodily injury, property damage and other financial/fortune loss (usually with a bodily injury coverage limitation of €8-15,000,000 for each bodily injured person).
Auto insurance is financial protection, and not just for the investment you made when you bought your car. After a really serious accident, bills for damage and injuries can easily reach into hundreds of thousands of dollars. If you happen to cause such a wreck, the victims could sue you. In the worst case scenario, assets such as your savings and home could be seized.