I'm not an electrician, but I have an older house that doesn't have all of this, but I'm learning because I've had electricians giving me estimates of what it would take to install a 3 wire (with ground) system in my house, starting with the box. There is currently a ground wire running from the box to the water pipe where it enters the house.
They will have to install a grounding rod from outside to the new box. They also said that there are 2 grounds, the primary ground is the one that runs to the water pipe and the secondary ground is the grounding rod outside.
If you detach the grounding rod ground, at least it isn't the primary ground, but your house is no longer "in code", and you may have other issues, such as insurance waivers that certain surge suppressors provide when the house is properly wired.
