I wanted to add here that another way of doing this that I have read about and now try to do myself is when you buy a spare, install it! Then use your original as the spare. That way you know how to install it, you know you have the tools to install it, you know you have all of the parts you need, etc.
Working on a boat isn't like working on a home project. At home you can just jump in the car and run to the hardware store to pick up that little washer you dropped, or the screw that the manufacturer neglected to send along, etc. On a boat it's often .. well, slightly more difficult to get to the hardware store.