I certainly would Baldy,I`ve opened and replaced watch batteries in cheap watches before but I would never attempt to open something like a tag or rolex!
The waterproof models usually have an Oring gasket that can be pinched and if the watch is gold,well if you look at it too hard it gets a scratch!
It`s well worth having the battery changed and the watch serviced every so often. I expect both of mine to require servicing and the omega will likely need a new battery as well.