How to add custom user group to add-on project roles in many existing projects?

Repeating Issues add-on project roles are configured with jira-users and jira-developers groups as default members. Admin can add new default members for each role as described in Jira documentation: Specifying 'default members' for a project role. Please note that changing a project role's default members does not affect the actual project role members for projects already created. It is only template when new project is created. Existing projects need to be updated following to this documentation Managing project role membership.

Admin can use Jira REST API to create changes in multiple projects using curl or using simple shell script (click to download). Just execute

 ./add-custom-project-role-actors --jira http://localhost:2990/jira --user admin --pswd admin --roleId 10100 --project PROJA,PROJB --actors '{ "group" : ["my-custom-group-name", "another-custom-group-name"] }'

RoleId can be found in url when follow instructions to Specify 'default members' for a project role. E.g. http://localhost:2990/jira/secure/project/ViewDefaultProjectRoleActors.jspa?id=10100