Actually, in most cases, it doesn't complicate things at all. He's free to change course or speed any old way he wants as long as risk of collision is not present. An often missed subtlety to the rules; there is no stand-on or give-way vessel if no risk of collision is present. Which leads to the court decisions that have held that, if no collision occured there was no risk of collision! You really can't win. (g)
While the words in extremis have gone away in the Colregs, they live on in the annals of maritime law. I recommend Farwell's Rules of the Nautical Road to anyone truly interested in how the rules have been interpreted and the meaning behind them in various situations.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.