Who you are is already a lock
The collected Origins page names six people you can play — Astarion, Gale, Karlach, Lae'zel, Shadowheart, Wyll — plus the Dark Urge, plus a custom face. An Origin comes with a private plot and a set of people who already have opinions about you. A custom face is quieter and freer. Race and body type lock when you leave the screen. Class can be reset later at camp through Withers; an Origin's background cannot. Pick the story you want to live inside, not the portrait that looks sharpest on the nautiloid.
Heads up. People reroll after Act One because they treated the first screen as a dress-up menu.