Active Admin + Rolify -- A simple example of modifying roles within active admin on users.

ActiveAdmin + Rolify -- Roles Administration

ActiveAdmin.register User do
  index do
    column "ID" do |user|
      link_to user.id, admin_user_path(user)
    end                          
    ...
    column :roles do |user|
      user.roles.collect {|c| c.name.capitalize }.to_sentence    
    end
    default_actions                   
  end  

  show do |ad|
      attributes_table do
        row :id
        ...
        row :roles do |user|
        	user.roles.collect {|r| r.name.capitalize }.to_sentence
        end
      end      
   end

  form do |f|
    f.inputs "User Details" do
      ...
      f.input :roles, :collection => Role.global,
      	:label_method => lambda { |el| t "simple_form.options.user.roles.#{el.name}" }
    end
    f.actions
  end
  
  controller do  	
    def update
    	params[:user].each{|k,v| resource.send("#{k}=",v)}  		
  		super  		
  	end

    def permitted_params
      params.permit user: [ ..., :role_ids]
    end
  end
end

Did this work for you?

It works perfect, thanks!