Dynamic coordinates on map

[tarawynne]

I have a map template where the data frame is in the Irish Grid(IG) Coordinate system.(Blue lines) .I have a grid created aswell showing ITM coordinates(Black). I want to show the centre coordinates of the map in the legend. currently I have them displayed as Irish grid (IG) but I want them to display as ITM. 

is it possible for the centre coordinates to read from the grid(black, ITM) rather than the actual dataframe(blue,IG)