How hard will it be to switch out some old, dated fixtures in my finished basement...?

that's the hard part about a drywall ceiling in a basement. you should have enough clearance for a can lite. my suggestion would be to take down a small section of the ceiling. check at your local home store. you can get lites that screw onto the side of the floor joists without making too big of a whole, then make the patch with a toe nailed board at the edge. ask them, they will explain