Depends on how straightforeward it is.does anyone know if fitting a shower is difficult?
A straight change can take 1/2 hour altering pipework etc can take a couple of hour.
Yours is simple you have exposed pipework.
water feed/electric supply.
Tritons tend to be on the right, as mira's tend to be on the left.
Changing that mains cable won't be easy as it buried in the wall.
So i would say that was part of an old install before the consumer to pullcord was changed.