I've always taught that turning a fuel pump off is not a function of altitude but a function of position and situational awareness.
Where are you and where you going.
Straight out? Downwind departure?
Night? Day VMC?
Locations off airport landing opportunities?
On a side note.
Replacing an engine doesn't mean that accessories are always new.
Everything external that isn't required to be replaced can be swapped from the 'old' engine.
No saying how many hours an engine driven pump may have on it.