When replacing spark plugs on a Ford Five Hundred is it necessary tochange boots

I highly recommend replacement of the spark plug boots.

If the current spark plug boots are good, then why do you need to change them out? Aren’t they there to just protect the spark plug?

Actually they prevent high voltage ignition spark from jumping to the surrounding metal spark plug tubes which will result in a misfire - the boots become brittle over time and like other parts need to be replaced periodically.