you shouldn't need to cut the rubber, the transponder will pull out of the bottom of the rubber holder. Did this with my wifes ex-mondeo before scrapping it so i could use the fob for the puma.
That's true... when i did it i managed to slip it into the new key without cutting the rubber but had to cut it out of the old one.... maybe it just depends on what the rubber bit is like...
When the fob is in two halves, press a screwdriver on the base on the rubber. If you give it the correct amount of angle and pressure the transponder will poke out of the top. Bit of a knack but no damage.