Of course, in the case of metallic material and alloys, heat treatment can modify their properties. These changes are induced by several mechanisms (depending on the material chemistry) : phase transformation, precipitation, recrystallization, recovery....). All these mechanisms will affect the material microstructure, which controls the properties.

It is a very general question! changing the materials properties with heat treatment depends on many factors such as prior microstructure, type of alloy, and so on.

But in general, heat treatment CAN changes the overall mechanical properties. its SIGNIFICANCE depends on those many factors ...