Welcome.
No, it is not possible to do that.
On UK cars, this spot on the instrument cluster is a permanent display of the current speed in km/h.
On non-UK cars, this spot on the instrument cluster displays the ambient temperature. On UK cars, you need to go through the instrument cluster menus to have the ambient temperature displayed, but you cannot have it permanently displayed at all times.
It has been like that for the past 20 years, since MB stopped fitting their cars with speedometers that have two dials, one for mp/h the other for km/h.
It is possible to convert the instrument cluster back from UK to non-UK, however, all that will happen is that the km/h display will be replaced with a permanent ambient temperature display (and you'll need to pay a specialist to do that, because it requires the use of MB STAR diagnostic computer). So, this will obviously not help you much.
You can, however, from the instrument cluster menu, choose to have the current speed displayed (in mp/h) on the central LCD display on the cluster - however, while you have the speed displayed there, you will obviously not be able to use the instrument cluster's LCD for anything else (e.g.navigation instructions, or mpg display).