Can I rebuild the bumpy torsion bar rear suspension in a Toyota Corolla to an individual suspension?

Answer 1

First you need to figure out why it's bumpy (whatever that means). Try putting some weight - 100 lbs - in the trunk and see if that makes a difference. Whatever your springs are in the rear, it is not easy to change the design.

Answer 2

You mean convert it from solid axle to an independant rear suspension? I've heard of more complicated projects, but you need to really know what you are doing. Both with suspension design and with a welding torch. Not easy and not usually worth the effort.