Friend, all you need to do is go to Ceria to grow out/shorten your hair. She's on Tavros, where you start the game, and is in a very obvious location for anyone that takes even a single minute to look around. She's available at all times.
Getting to exact length values is absolutely pointless, because the only thing the appearance screen and parser describe when referencing the PC's hair are the benchmark hair lengths. No matter what the exact length of your hair is, it will only be described as whatever benchmark range it falls into, limited exclusively to: short, shoulder-length, long, back-length, ass-length, knee-length, and ankle-length. In this way, Ceria gives you absolute control of your hair. You cannot customize it in a meaningful way beyond the services Ceria provides except for mod-specific hair flags like mane or latex that are obtained from the associated TF's.
When Aislinn is implemented, the exact same level of control will be provided for beards in the exact same in-game location. Aislinn will allow the player to hit every beard length benchmark, including: stubble, short, medium, long, chest-length, and waist-length. Her services will be half the prices of Ceria's, too.
Yes, getting a beard right now is a completely ass-backwards process, but that's the entire reason I wanted to add another employee to Shear Beauty to handle them properly. Getting a beard right now is fairly pointless anyways, because there's no one in the game that can style them, color them, or really do anything with them at all, and most TF's don't really affect them.