I have them on my car. No clam off needed (although it would be easier with it off )
The originals were removed by popping out the indicators/blinkers. That will give you access to the screw that goes through the top of the original plastic side grills. I put a towel on the car and flipped the indicators out of the way as the hole was used to help mount the new mesh grills.
The shape of the clam has a little cutout that i had to file down to make the hole as round as possible. The new mesh grills then had to be shaped to fit the curved hole (just by hand). Then you need to apply some of the sikaflex sticky stuff and hold it in place until it dries. NOTE: It's hard to get off your hands
Centre grill: The original removes easily. The new one has to be sikaflexed in place. Actually i still havent sikaflexed mine and it just sits in there nicely
I areas i have circled below are:
1. Side grills - where i had to file down. There is still a little divet where the original grill mounted even after my filing.
2. Indicator - bottom of indicator has a little hole so u can pop it out with something. Think i used a small screwdriver.
3. Top of centre grill - after the new mesh is installed you will still have the little metal things that the old grill connected to. I don't even notice them so just left them.
4. Bottom of centre grill - because the new mesh sits back further than the original grill you will see the holes that the old grill connected into. I don't notice/care about these. Less noticable on a darker car obviously...