Your name is an important source of information for your fellow clones, as it will show which regiment/battalion you're part of and your current rank and name.
New recruits will join the Infantry division and will have to follow one of the following name formats:
CT PVT<####> <name>
Your name must be changed if you switch regiments/battalions, if you get promoted/demoted or if you decide to change your name (must be logged by a CO).