No, simple is often the best, but the lighting for the speedo I believe comes from behind the dial faces and shine turn the speed markers on the dial face.
Now the people who look after car rego ( tax) over there might demand that the MPH are scaled at a set rate e.g. a minor marker for every 5 mph and major market at every 10 mph. This means just lining up the KM/h hour markers on a new sick over dial face may not give the right spacing in MPH.
Also we can’t just use a second hand mph dial face as some of the icons (turn signal, high beam) are in different places. But if a fully custom one were made then all would be good but the gov might also require the total distance travel to be mile not KM.
I really don’t know the full requirement and how tough they are over there, but I can tell you our people require the speedo to be fully changed over, ie no stickers are allowed to be used and they don’t care how hard this is to do.
Snoopy
Ps you are right about the MINI does not care if you have KM/H or MPH, as the MINI is based on the metric system it must convert it to MPH on the fly as it store evey thing in KM.