How do we send dunning letter with different subjects and email body for the same customer account a

How do we send dunning letter with different subjects and email body for the same customer account at different stages, for example

letter 1: a Pre delinquent letter , we want to send it to customer to remind their payment is due soon, and we would like the subject of the email to say "REMINDER" and the email body worded accordingly.

then if the customer still does pay their invoices on due date and pass the due date, we want to send,

Letter 2: a Overdue letter, we would like the subject of the email to say "Your account is OVERDUE" and the email body worded accordingly.