Does one size saddle valve fit 1/2 & 3/4 inch copper pipe? Can you replace a leaky saddle valve with a new one in same location?

Saddle valves have been around for a long time and under the sbcc [southern building code congress] they have been illegal. And now, the ipc [international plumbing code] has taken over and there are now legal. If the pipe it saddles is not corrupt then you can simply replace it. Turn the water off first.