Frank is the expert so what he says is gospel for me...
In the past I take in my Casio G-shock and I make it real clear. I look at them in the face to make sure I have there full attention.
I want the battery replacing...
I am a diver.
Please carefully remove the o-ring and clean it- do not pull on it because you will deform it. Grease it with whatever you have and put it back together.
Also with the G-shock there is a spring behind the plate- please do not loose it…
Then they claim they cannot test it and I say yeah, yeah, yeah.
I am hoping to do this myself soon.
I have never had a problem with two battery replacements.
Although, I tend to destroy Casio G-shocks water, rocks, mud, diving in everything possible.
I would call Casio- ask for technical department and ask specifics for recertification.
The only thing I know that was ever freaky was a Helium escape on some of the Rolex and specialty dive watches.
The only drawback could be if there is an onboard pressure transducer?
Andrew