Complex sentence: Thrawn's 501st was an elite unit charged with the defense of the Hand of the Empire (also called as the Empire of the Hand in some novels), however it was no longer completely composed of Jango Fett clones.
Split into simpler sentences: Thrawn's 501st was an elite unit charged with the defense of the Hand of the Empire (also known as the Empire of the Hand in some novels). However, it was no longer completely composed of Jango Fett clones.