Programming pattern / architectural question

Question

I am currently working on a project where I have a BankAccount entity for some other entity.

Each bank account as a reference to a bank entity, an account number and opt

Answer 1

Rather than the IBAN number being a simple string, what if it was an actual class? You could implement validation in the constructor (if validation has no external dependencies), or you could use a factory to provide IBAN instances (if you need external validation). The important thing is that, if you have an IBAN instance, you know that it's a valid IBAN number.

Should BankAccount actually have a mutable IBAN number? I'm not terribly familiar with banking, but that sounds like a scary idea.