There are 20 - 8 foot sections of railings that surround the deck in my backyard which surrounds an above ground pool, a gazebo, and a hot tub. There is a flat piece of decking screwed in on top of each of the sections and I am in the process of replacing those top pieces. Our deck is over 10 years old as is our above ground pool and hot tub and for all intents and purposes, all of it has lasted longer than I thought it would. We stain the deck every 3 years so I suppose that is why it has lasted as long as it has. While all those top boards do not need replacing, I am replace them all anyway so it will look the same when it comes to staining them next spring... it is best to let wood weather for a year before staining it, we've been told so that is what we do.
This is not hard work other than moving the wood from one location to another... I unscrew the old boards which so far has proven not to very difficult at all. Then, I lay the old board on the new board, draw a line at both ends if there is an angle, then I cut. The new cut board is taken to where the old one was removed and screwed into the post at both ends to prevent warping due to temperature fluctuations and rain.
After the railing is done, there are 2-3 boards on the floor of the deck that need replacing but that is it and fairly amazing since the deck, as mentioned before, is over 10 years old.