Redmine

Hello, i have extended the code from
https://github.com/theodoreb/redmine_user_pain
a little to fit my needs.

Now i am stuck with roles/permissions.

i want to check/uncheck the view permissions under administration/roles. i managed to edit my plugins init.rb so that it shows a checkbox for my plugin. but the hook is called any time for any user. how can i prevent this for some roles?