Inboard seat belt latch and rear wiper replacement

I'm not new to Land Rovers, having a Classic LWB and a Discovery, but the P38 has me scratching my head on a few things. How do you replace the rear wiper blade and NOT disconnect the battery (not a wise thing to do on a P38...)? How do you replace the inboard side of the outer right passenger rear seat belt buckle? There is no clear access. There are screws on the metal seat pan underneath and one screw on the plastic cover, visible from above. Since seat belt anchorages are supposed to be very secure, I cannot imagine that these are the securing points for the latch!