@sbglasius thanks!

grails:
    config:
        locations:
            - optional:file:${PATH_EXT_CONFIG:-/app/config}/application.yml
            - optional:file:${PATH_EXT_CONFIG:-/app/config}/application.groovy
            - optional:file:${PATH_EXT_CONFIG:-/app/config}/custom-application.yml

assuming that in

#application.yml

a.list:
    - name: example1
      description: desc1

and assuming that in

#custom-application.yml

a.list:
    - name: example1
      description: desc1
    - name: example2
      description: desc2

which one will should take precedence also is

optional:

valid in your plugin i dont see any reference, can i dispense with it