How to implement a dynamic referral program?
Separate data and business logic.

A database is a repository for data, so put those numbers in a table (let's call it Creds), possibly with date ranges of when they are applicable.

Your application code is where you build the "business logic" that interprets "referrer", "referree", "first time", etc, based on the data.

For example "first time" would come from some other table that, for example, has the entire list of "referred spends" for a user.  You would write a suitable query to determine "first time", then use Creds to and the current date to decide how much credit to give a user.