I just replaced my 15 year old widemouth skimmer due to a small crack after waiting for it to come off of backorder (but that is another story for another time).
My water level was all ready below the skimmer level so it was the time to do it. The whole process takes less than 30 minutes. A second set of hands is also helpful if your skimmer is attached to your wall on the exterior as ours was.
Here is my 12 step program, Hope it helps
1. Lower water level below the skimmer level.
2. Remove the hose or piping from the skimmer.
3. Remove faceplate from the cover location.
4. Remove gasket(s) being careful not to tear or stretch the liner.
5. Remove screws that mount skimmer to the steel wall. This may require a very short screwdriver and again be careful with your liner.
6. Clean skimmer location of wall and liner to remove any debris or other items. Check steel wall for damage and repair as needed.
7. Attach new skimmer to steel wall. Make sure screws are stainless steel.
8. Place one new gasket on each side of your liner at the skimmer opening and line up with the holes from where you removed the screws. Place a couple of screws through the cover plate and then push them through first gasket, the liner and second gasket. (I used the top two corners) Line up the cover plate, gaskets and liner combination to the mounted skimmer and start screws only a couple of threads. This will allow you to see the line up for the rest of the screws.
9. Place the remaining screws in place making sure to push them through the original holes in your liner and each gasket. Start each screw into the skimmer again only a couple of turns.
10. Once all screws are in the correct place and started you can begin to tighten the screws in a systematic approach. Tighten the screws a few more turns each starting with the screws in the center and moving towards each edge. Such as center top, center bottom, next left top, next left bottom, next right top, next right bottom. You should be able to watch the gaskets squeezing the liner as you tighten the screws and it should be smooth with no buckles in the gasket. Once that is completed go back to the center screws and tighten again until all of the screws are flush in the cover plate.
11. DO NOT OVER TIGHTEN the screws. You only need to compress the two gaskets against both sides of the liner. If you over tighten the screws you could crack your face plate.
12. Reattach hose or piping to the skimmer, fill the pool and enjoy.
Once installed in this manner you should not have any water getting in contact with the steel wall. Your liner is sealed between two gaskets and the water should not be leaking on the wall or pool side to get behind your liner.
Dennis