Can I change lower unit oil while in the water

I have a pair of merc 60 4 stroke (EFI) on a houseboat and a hefty price to pull it out of the water. My last lower unit oil change was when the dealer winterized them in fall of 2018. I didn't make it in the water last season so no hours on this oil change.

1) Is lower unit oil the same as the engine oil where changing every 12 months (regardless of usage) is 'required'?
2) If so, is it possible to do 'in-water'? ( I have jack plates and with a full tilt I have access to the ports.)
3) I'm a slow boat and proud of it. Does the fact that I almost never run the RPMs higher than 5k have any effect of the need to change oil in the above case?

Thanks!

A lot of good gear oil is thrown out every year.------I would say remove the gearcase ( use a dingy ) as a work platform.-------Pressure test gearcase.------Change oil on the work bench.------Install new impeller.------Put gearcase back on.

racerone said:

A lot of good gear oil is thrown out every year.

Click to expand...

The original post should have included the fact that I'll be pulling the boat for the season in another few months anyway. (Am in Wisconsin where the season ends mid October)

So I face a mid-season $600 expenditure just to pull it out of the water for these lower unit oil changes. All area marina mechanics are already scheduled a minimum of a month to six weeks out so pulling a couple gear cases now is not feasible.

I have to think that operating at a low RPM like I do doesn't place the same stress on the gears as running WOT like most boaters do. So I'm here  looking for someone to convince me that gear oil breaks down just by time passing. (again... no usage in 2019).

thanks again.

Don't worry about your gear oil breaking down.------The gear cases are sealed.-----The gearcases are water cooled too.

Thanks for that -- I'll sleep better.