What you really want to avoid when drilling out a rivet is ovalizing the hole by drilling right through the rivet, slightly off center. A hole that is not quite round and bigger than it ought to be will weaken both the spar and new rivet. The best way to do the job is to drill off the head of the rivet and then drive the rivet through the hole using a punch. This is the way airplane mechanics do it, for good reason.
First, drill off the head using a drill bit slightly larger than the diameter of the rivet. Once you've gone far enough, the remains of the head will start spinning around on the drill bit. Try to not go further than you need to, but in the worst case, you'll put a slight chamfer on the outside of the hole. Here's what you'll end up with:
Note the head of the rivet on the drill bit...
...and the countersunk hole in the body of the rivet.
Now it's time to punch out the rivet. I like to use a punch that is a slightly smaller diameter than the rivet. If the spar was built properly with a corrosion inhibitor like Lanocote, the rivet will slide out like butter, with one tap on the punch. You can also smell it, even on this 20 year old boom. If a Lanocote wasn't used, it'll take a couple of knocks with hammer to punch it through.
Fish On Fridays. - I always fall for a fly, especially if a pretty young wahine is at the other end of the line.
4 days ago