I've drilled out similar but not exactly that location, it's tricky to not elongate the hole and make it even harder to set the new rivet. At least your rivet is only partially set so it should be easier to remove.
The key is to drill exactly perpendicular through the dead centre of the rivet.
I use an automatic centre punch first to emphasize the dot in the factory head.
Then use a sharp pilot drill e.g. 2 mm to go almost all the way through. A square can be clamped beside the rivet to help visually guide the bit to be perpendicular.
If the rib is in the way of the drill motor and cannot be flexed to the side then a 12" long bit may help.
After drilling the pilot hole I drill through just the factory head with a 1/8 bit and use the shank of a drill to snap off the factory head.
Then the rest of the rivet should knock out with a small pin punch. Sometimes I use a blunt panel pin knocking in the bottom of the pilot hole to do this.
Take it slowly and carefully and you can do it!
Paul vS (yes I'm also a Van)
Building RV-6A #22320 O-320 FP. Wings and tail complete, fuselage almost done, working on canopy.
Flying my Aeroprakt A-22 STOL and the aero club's RV-9A while I build