By carefully heating the springs you make them soft so you can reduce the height & can give the low look,since many of the past posts were just about obvious ground clearance issues i would consider this a Start or a suggestion to "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