Well that was hilariously easy
Punch a hole into the red bit with a screwdriver and then hack away! Literally takes 2 minutes to rip it all out.
The only awkward bit is seating the new grommet into the spoiler as it's quite deeply recessed. I'm not sure if folk bother doing that but I did, just in case it prevents water from getting into the car.
Skill level - 1 spanner
Tools required - Hammer, screwdriver, long nose pliers and if you have them, a right angle pick to help you pull the old grommet out.