Fair point Dave if you can get away with the lower value although not sure you included all loads on that fuse in your calculations. I understand your concern following PCB repair but note this fuse feeds only the rear fog relay coil on PCB which you say didn't fail during the burnt land episode. Note also the PCB has other power feeds including a 20 amp fused permanently live one!
Apologies if I appeared a little harsh with my criticism but it did seem an incongruous move to reduce fuse value after your previous overheated fuse issue in this location despite switch to LED's.
Regarding MMC making the wrong fuse choice, I imagine they erred on reliability especially given same fuse values for the sidelight circuits are used on later cars.
