No, that's not what's going on. And your base assumption is wrong.
There are many, many cells in our body that aren't replaced after 9 months (brain cells or bone cells for example).
Aging happens because of many factors, one is damage to the DNA. That is a natural consequence of living, not of personal beliefs.
And a person with multiple personality disorder can't change eyecolor.
Multiple personality disorder can if u look this up u will see I'm right
It's impossible to change your eyecolor without artificial means and even then not by just switching personalities
u should look this up and be proven wrong as their is documented cases this happening