A really good analogy to answer this question is that of 4K technology. In order for you to maximize and get the full experience, each device you use must have 4K technology. For example, if your TV had it but your video game system does not, the output will not be natural 4K. Understand, now take this concept and relate it to attempting to change batteries or your SD card in your waterproof camera underwater. The camera may be waterproof, but the batteries and SD card are probably not. Even more so, when you open the port cover, it can flood the camera and internally, it is not going to be waterproof.
In short, you should never, ever attempt to do this. Unless you are 100 percent certain each component is waterproof, which is pretty much all but impossible, open the cover and change the components above water.