The speakers come with 4 small strips of double sided tape to help with the grill installation. The grill has a tight fit and I didn't have to use the tape. I would peek through the holes and see if you can identify where the tape is.(The instructions say to use them in the corners) Take a paper clip and bend it so you can fish through one hole and back up through another one and gently pull out. If you do this close to one of the strips of tape you should be able to separate it one corner at a time. Hope this helps and you don't damage the grills.
They are not water resilient, however, depending on the surrounding atmosphere. I would as long as there is not direct exposure to sunlight, water, or extreme temperatures.