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. 
CTP insurance is compulsory in every state in Australia and is paid as part of vehicle registration. It covers the vehicle owner and any person who drives the vehicle against claims for liability for death or injury to people caused by the fault of the vehicle owner or driver. CTP may include any kind of physical harm, bodily injuries and may cover the cost of all reasonable medical treatment for injuries received in the accident, loss of wages, cost of care services and, in some cases, compensation for pain and suffering. Each state in Australia has a different scheme.
Police forces have the power to seize vehicles that do not have the necessary insurance in place, until the owner of the vehicle pays the fine and signs a new insurance policy. Driving without the necessary insurance for that vehicle is an offence that will be prosecuted by the police and will receive penalty. Same provision is applied when the vehicle is standing on a public road.
The immediate impounding of an apparently uninsured vehicle replaces the former method of dealing with insurance spot-checks where drivers were issued with an HORT/1 (so-called because the order was form number 1 issued by the Home Office Road Traffic dept). This 'ticket' was an order requiring that within seven days, from midnight of the date of issue, the driver concerned was to take a valid insurance certificate (and usually other driving documents as well) to a police station of the driver's choice. Failure to produce an insurance certificate was, and still is, an offence. The HORT/1 was commonly known – even by the issuing authorities when dealing with the public – as a "Producer". As these are seldom issued now and the MID relied upon to indicate the presence of insurance or not, it is incumbent upon the insurance industry to accurately and swiftly update the MID with current policy details and insurers that fail to do so can be penalised by their regulating body.
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.
You’ll notice that none of that liability coverage pays for your car or injuries, nor for any injuries your passengers sustain if you cause a wreck. This is why many people — particularly those whose car isn’t yet paid off — want “full coverage” car insurance. This isn’t actually a type of coverage, but instead typically refers to policies that include liability coverage, plus comprehensive and collision coverages.