The FR springs are harder so you do loose a bit of comfort.
They are only 20mm lower than the comfort suspension.
Springs and dampers are designed to work together. Changing just the springs could give unpredictable results. It could be fine, it could work well, but you won't know until they're on the car.
It will certainly affect any warranty you have and your insurance. You could opt to not tell either of them but it's a risk. I don't think they'd spot the change if there were no other modifications to the car but who knows.