Well, sure, I cannot disagree. If OP has a drill press and a 10 mm bit, then that is the way to go. With that in mind, ideally the ring should have a 10 mm hole, enlarged to 12 mm about halfway through.
If he's working with hand tools, though, I stand by the reamer suggestion (a rat tail file is also an option, but requires a bit more skill). In practice it is pretty easy to enlarge a hole in aluminum, a little bit at a time, trying the bolt repeatedly, until the bolt will go through. it should be a tight fit.
He doesn't need a press, just a vice with a vertical v-goove (common). Hold the bit in the v-groove with just a mm or two of the lips showing, place the chainring hole on the point, and turn the ring, keeping it flat to the vice jaws. Once the bigger hole is started, raise the bit in the groove a mm or so and do it again; repeat as required.
And if he wants a stepped hole he need a counter-bore, not a bigger drill, that's a tricky part to find with the correct diameters. Much simpler to go with a straight hole and a longer bolt, if frame clearance will allow.