as defined in http://devops.wcm.io/conga/yaml-definitions.html it is possible to insert the keyword merge in lists of array configuration parameters. this works well in simple cases, but does not work in complex cases, e.g.:
list is defined as global param in environment, including merge. additional list items are defined on node live. in this case it may happen that the values from the global list are included twice
in the previous example some list values are defined additionally as default value in the role itself. they are not included.