Yes having a liver transplant is major surgery.
The liver transplant surgery takes between 6 to 12 hours for the actual surgery to be performed.
The liver transplant surgeon will remove your old liver and then replace the old non working or diseased liver with the donated liver.
Hopefully the new liver will take and most do but there's the potential for the liver to not take and then you may need another liver transplant surgery.
The amount of liver transplants you can have in your life is as many as you need.
However there is a limit to the amount of available livers that can be transplanted and not all livers from all organ donors will work in all bodies.
So you're limited to the amount of livers that are actually available.
Most people have at most of 2 liver transplants in their life and some people may not even find a liver to be transplanted.
If you have liver disease and cannot get a liver transplant within a few years to 5 years then you might die depending on how severe the liver disease is.
Most people only need one liver transplant done and then they go on to live a long life.
But some other people may have a rejected liver transplant and need another liver transplant.