Most speedometers marked in MPH also have a KPH scale, usually in smaller
characters or a different colour.  I expect that most cars in use in
Ireland still have speedometers marked in MPH; the change to metric speed
limits only took place in January.

The easiest approach might be to get (or make) a simple conversion table,
and memorise the MPH equivalent of common speed limits.

<http://www.gometric.ie/> looks useful.

I think there could be legal implications to trying to re-program or
mechanically alter your speedometer; if you really want to do that, consult
a garage.

<snip>

Before I became familiar with resetting the trip meter, I once made
the speedo units change from mph to kph by accident.

I can't remember what I did- was it hold down RH button for a long
time without? with? the engine running?- but be assured that it *can*
be done using one of the buttons on the speedo panel.

As for the odometer question- sorry, I don't know for sure, but I'm
pretty certain that it stayed in miles for me- though I didn't have
the speedo in kph for even a minute, and certainly didn't travel any
distance with it like that.

From what I can remember you view the total mileage screen, press the button on
the right of the display until the word MILES flashes then give one press of the
same button and MILES changes to KM you then have to turn off the ignition and
when you turn on again speedo and odometer read in KM. The process to return to
MILES is similar.

Apologies if I have not remembered the steps correctly.