The self is not a stable entity
The self is a process
Obviously you can learn things that can change your core self-concept (and develop your skills, get promoted at work, etc.), and in that way yes, the self is a process. That said, many aspects of the self are stable. Your demographics, genes, etc. don't significantly change. Your gender doesn't change. Before anyone tries to jump down my throat, no this is not transphobic-transgender people's brains were always the gender they publicly transition to. Aside from that, your height stops changing after adolescence. Your age constantly changes, but your demographic of age (generation) doesn't. Your skin color doesn't significantly change. Introversion/extroversion doesn't really change (even if you learn to be more outgoing/quiet). Your humanity doesn't change, even if you become a criminal, soldier, or enemy of the state. Obviously your marital status can change, but personality-wise, you pretty much know whether you'd like to be married eventually by no later than 25 (even if you despair of ever finding someone to marry). There is no solid proof that you can change your sexuality even if you are motivated to. In fact, I'd say most personality traits are pretty stable, but opinions and ignorance can change frequently.