Easy to remove but can be a bit fiddly to get back in. There's plastic lugs that sit in sleeves behind the card that have to pop into the bodywork. I removed one of mine (offside) and it was fairly easy to remove. Getting it back on however is another story. I have at least one lug I couldn't be bothered putting back. The door seals play a part in holding the card neatly too.
I got all this ahead of me since I might fit my 6x9's in the rear door cards when the time comes....the fact they are hard to replace might put me off though :laugh: