If you want to install the carnards without drilling holes, then use 3m tape. If you want to remove them later, then just pull them off. I personally would not install these on the car, but I don't own your car and neither does anyone else that has commented. Personalize your car to make yourself happy, not everyone else. If that look is what you like, then install them.
I highly doubt you would ever get a ticket for 2" carnards protruding from your bumper. If the carnards come that close to a pedestrian, then you were probably trying to run them over.
Remember, no points are given for glancing blows. Only direct hits.