Impeller change out

[BigRock44]

So I am gonna try to change out my impeller on my 2014 Yamaha f150 outboard. Doesn't seem too terribly difficult but my main concern is putting the lower unit back on when I'm done. Apparently I'll have to make sure to have the small gear shift rod on the lower unit line up perfectly when I'm sliding the lower unit back on so the splines mesh correctly. I just don't want to have any gear shifting issues out on the water after I launch.

1- How do I know if the gear shift rod meshed correctly into place without having to launch the boat? Is there a foolproof method to doing this?
2- Should I have the gear in neutral or forward during the entire replacement procedure?

Anyone have any experience with this? Any help would be greatly appreciated. Thanks very much.