I changed the side grills and gills on my E90 because IND painted the honeycomb/mesh in gloss black for me.
When I removed them I pulled the fender liners and unclipped them by reaching in and releasing the tabs and then pushing them out..... they came really easy. There is approximately 10-12 screws in each fenderliner so they are no big deal to pull out of the way. The only other thing is you have to remove one nut on the right side which holds the windshield washer bottle in place and then slide the bottle toward the front of the car a bit. Total time after the wheels are off is only 10 minutes per side. The great thing about doing it this way is there is no risk of damaging paint and the gills will unclip from the grills quite easy once they are removed.
2011 E90 M3 ZCP - Individual Moonstone/Individual Amarone Extended/Individual Piano Black With Inlay:LINK!!!
1994 Euro E36 M3 Sedan - Daytona Violet/Mulberry:LINK!!!