"lowering the ground clearance" as his purpose for doing this is not practical but visual appeal.
"not practical but visual appeal"
Dear, he (ofcourse each one of us) doesn't want the car to be in "showcase" with visual appeal rather than practical.
-Heating the springs: not sure that both springs will get equal amount of heat. If not, just think of the end result.
-By making them soft with heating, if the kerb weight of the vehicle could bring down the vehicle to some extent, what would happen with 5 on board and over a hump?
-By heating there may be deformation in springs (especially eccentricity among the coils) this will spoil the suspension geometry. End result: ride and handling will be poor + premature failure of wheel bearings + tyre wear