Well, I replaced my second window. Also upstairs, but this time without a porch to stand on.
I had NO idea that an extension ladder would bend and sway that much! I ran into two hiccups this time - the window sill was pretty rotted. Wood epoxy has come a long way - first I treated the wood with a drying agent to dry out any moisture still in it, then I filled it with a two part wood patch epoxy that hardened like steel afterwards.
The second problem was that the black stripe that was above that window on the outside wasn't just the wood behind the siding like I'd always thought. I literally had a 2 inch high, 32 inch wide HOLE in the side of the house from where the people putting up the siding screwed it up. It was large enough that there were leaves inside the wall. I filled the gap with expanding foam, then covered with a piece of trim, painted white.