I am tasked to care for a mature lemon tree, ~8-9ft, planted against a house.

It is loaded with nice fruit, but has a very scant shell of (healthy) foliage and a bare interior. The yellow/green ratio looks very unbalanced.

Was told the tree has been regularly bearing fruit, so would it be better to leave well enough alone?

Otherwise, what pruning/fertilizing techniques might I employ to ensure long-term health, vigor, and bearing of this tree?

Also: Would keeping the tree well harvested encourage foliage growth, rather than leaving lots of ripe fruit on the branches?

Thanks!