I am considering a style change to the bathroom which will include the changing of all taps and the shower mixer valve.

I have seen the style I am after but am unsure of the procedure for replacing the mixer valve. Taking it that the gap between the hot and cold entry pipes are the same on the new valve as the old one, is it simply a task to isolate and undo the supply pipes and fit the new valve or am I still going to have to make holes in the walls to gain access to the pipework?