Is it permissible for a husband & wife to act out fictional scenarios during foreplay, such as pretending one is a doctor or another made-up character and saying made-up things to the spouse according to their roles e.g. saying that they’re a doctor, when in reality they’re not but spouse knows this

Yes, this is allowed. What is between a husband and wife of enjoyment is broad and permitted, except for what the Shariah specifically forbade. If the role is an imaginary character and involves nothing independently forbidden, it is permissible, but if it means one of you brings to mind a specific real person, or the act imitates something forbidden in itself, then it is not allowed. Allah knows best.