The term "sharpshooter" had a more general meaning in the mid-19th Century than it does now. It could mean either a roving precision shooter like the modern sniper (a term that did not come into use until late in the century) or a light infantryman who specialized in the petite guerre: scouting, picketing, and skirmishing. The modern sharpshooter appeared in Central Europe around 1700 (the term comes from the German scharfschutzen), so the book begins with a look at how European armies employed both light infantry and sharpshooters through the Napoleonic Wars and the Mexican War in America to the “Minié revolution” in firearms just prior to the Civil War.
To this we might add the other meaning of the term in 1861. That is an infantryman armed with a Sharps rifle. Col. Hiram Berdan's sharpshooters were armed with this weapon.
I have not seen evidence that Confederate units listed as "sharpshooters" were organized, trained, armed, equipped or deployed in action any differently than other infantry commands.