Jedi: Survivor's Character Customization Makes Perfect Narrative Sense
You're on the run. Have been for years. An overwhelming force pursues you, limitless in its resources and hunger for domination. You never stay in one place long, yet wherever you go you hinder the opposition in some way before you disappear into the shadows and strike again from elsewhere.
Such is your life as Cal Kestis, a Jedi Knight and survivor of Order 66.
Moving around isn't easy when you're the most wanted man in the galaxy and the Empire is nipping at your heels. So what better way is there for a master of the Force to disguise their tracks than become a master of disguise!? Jedi: Survivor knows this and has your immersion covered.
Unlike its predecessor Jedi: Fallen Order, Jedi: Survivor goes all-in on the customization by allowing you to tailor Cal's appearance at any time using hairstyles, facial hair, jackets, shirts, pants, lightsaber styles/materials/colors, and more. Forget the High Republic, become a Jedi of HIGH FASHION. Or mix and match your outfits so badly, it looks like the galaxy's most wanted man dressed himself in the dark while late for an appointment.
How is the Empire going to track someone who is clean-shaven with a crew cut in a poncho one day, but the next day sports a mullet with a full beard, bomber jacket, and sweatpants?
The Force is inherently mysterious, and the Jedi are always learning new ways to channel it. Cal has gone beyond many a Jedi Master in figuring out how to channel the Force in such a way that he can spontaneously grow or lose his hair at will. The Empire hates him for this one simple trick!!
As you can likely tell, I'm joking. There's no in-game explanation for Cal's physical customization or fashion options. Though it just....fits. People on the run change their appearance often to avoid detection, and we can do that too with Cal. The Force works in mysterious ways, and there's a wide variety of proven Force abilities, such as allowing Jedi and Sith to glimpse the future, move incredibly fast, jump in mid-air, shoot lightning out of their hands, influence minds, and reportedly even stop death...although that last one isn't a story the Jedi will tell you.
All Force powers considered, I don't think it's outlandish to think that Cal can use the Force to affect his own body and the rate at which he grows hair.
I haven't noticed my appearance directly affects anything in-game as of yet and doubt I will, but I like to think that the ever-growing cast of characters you familiarize yourself with are simply used to Cal's chameleon-like ways. He's just another quirky character within the colorfully classic Star Wars cantina.