What kind of things were you thinking of?
On my old R53 Gen1 I had the underside coated in Waxoil to stop corrosion. You shouldn't need to do anything with the paint, other than repairing stonechips etc.
Remove two torx screws either side of the speedo at the bottom. The speedo will then slide off. You can unplug the electrics if required. Then remove the screws on the back of the speedo to open it up. My knowledge stops there i'm afraid. Let us know how you did it!