[logback-user] Using external logback file

Hello all, I need to use an external logback file for the logging configuration in my grails4 project. As I see the external logback file replaces completely the logback file in the project. Is there a way that it overrides it instead of replacing it? Which means the external logback file can be an extension to the internal one... we have this case that each customer has his own logging config but we still have our basic logging config that needs to be used for all customers so to avoid repeating it in the external logback file, it would be good if there's a way to override the internal logback file instead of replacing it.. Thanks in advance! All the best, Joud