Grind..? Yeah you just need to take it to someone who understands metal.
You can easily drill aluminium - use the appropriate size drill bit and guide in a drill press to align it to the existing bore. If you're drilling out a spacer accuracy won't be critical, but if it's a load bearing part you probs don't want to be taking out too much metal. Aluminium is not that strong
You mean you're wanting to put a larger axle through the wheel? You're going to need a drill press. You need to know the diameter of the axle that you're fixing to put through the hole. And you'll have to bore it correctly with a drill press. The problem that you're going to encounter is if you try to do that the bearings will no longer fit. Unless you know how to use a milling machine to make new bearing holes you're going to have quite a project in order to do that. I'd stick with the same sized axle and bearings unless you're quite skilled in mechanical things