Dent on earpiece Speaker Grill

To Bryant's point, yes, any action here will make the phone less water resistant. Having never been disasembled, I would consider the above iPhone to be “decently water resistant.” As soon as the top assembly of the phone is popped of the metal frame, the adhesive between the two halves will stretch and tear, resulting in the phone being “ barely water resistant at all if immediately reassembled.

This is why is good to replace the adhesive with a new gasket after completely stripping the old glue. If you really remove ALL the old adhesive residue from the frame and screen, use a new gasket that has no imperfections, avoid fingerprint oil contact on either side, and use a little heat/compression after closing, the phone can be made “decently water resistant” again. Precut glue strips for the frame are easy to find for a couple dollars.

However, to replace the metal grill just behind the screen cover glass, several layers of adhered bariers in front of the speaker with near to be peaked away. I do not think if it's practical to make an iPhone 7 earpiece speaker hole water resistant again, at least not as a DIY project. There are too many layers and buying the correct precut glue strips used in the original assembly may not be possible. So if you feel the need to replace the grill, know that it would be for cosmetic reasons only and the phone will be more easily compromised by liquid if submerged.