sorry if late for the party,
I used to remove the old one, prior to putting on the new one, as they say to remove, I found just sticking it on is fine... BUT.... what I used to do is below.
I found a chisel, narrow head, just under the sticker, by hand pushed takes it off.
I've done it 3 or 4 times with no problems
I don't have a heatgun, but a hair dryer does not have enough heat and a heatgun could damage the plate. After a year it goes rock hard and is crusty,
yup a narrow chisel used with care will do it, I'm in the GTA and would be happy to give it a try (FOC), you'd need to bring the car over to me though.