Does it have a 10 year battery

If it's anything like my original 1989 Casio DW5600 G-Shock, the battery will last a lot longer than 10 years. Mine is still working after THIRTY years.

When you replace the battery, do you replace the seal ?

From other G Shocks I’ve owned only if a new seal is needed. Watch repairers will also point out the water resistance integrity may be lessened.

Is this the g shock watch that's certified by nasa?

No but it is the original g shock from the 1980s - buy it you can’t go wrong. CR

Ok for scuba? (I know officially not but I've taken much cheaper casios to 30 metres withut a problem)

I am not a diver and I did not dive with this watch, but it is good for 200 meters (on paper anyway) so it would be good for diving. As far as I can tell: it is clearly one of or not the best and relailable watch that I ever had. After 6 years it is still going. And this type was also used in space as well so it would probably work as a scuba divers watch