It is interesting to see how different people go about solving the same problem. For myself I never came to either solution provided here for dealing with the offset created in Inkscape when changing the pad/ring size.
Here is my solution. In this example we will change all through holes from 1mm hole with 0.5mm ring to 0.8mm hole with 0.5mm rings. As we can see from the changes you will end up with rings that are 0.2mm smaller in diameter than the original rings. So we go through the SVG and change all the rings to be the new size and then move the entire Copper layer up and right by half of the change in diameter. So in this case we move the entire group up and right by 0.1mm. If we had made the Rings larger we would move them in the opposite directions.