Active admin habtm new button text change

user.rb

class User < ActiveRecord::Base
  has_and_belongs_to_many :user_groups
end

Similarly, user_group.rb

class UserGroup < ActiveRecord::Base
  has_and_belongs_to_many :users
end

Now the active admin page for user groups is as shown below:

ActiveAdmin.register UserGroup, as: 'UserGroup' do
  form do |f|
    f.inputs do
      f.has_many :usergroup_users, as: 'member user' do |user|
        user.input :user_id
      end 
    end 
  end 
end

Now this will create the user group form with fields for adding users to the new group. The button for adding new user to the group will be Add new User Group User. I want to modify this button label to something else. How can it be implemented?

Part of my problem is solved when using:

f.has_many :usergroup_users, heading: 'Add User to Group', as: 'member user' do |user|
...
end

This will change the header part to the required text. But the button label is still be a problem.

f.has_many :usergroup_users, new_record: 'Add member user' do |user|
...
end

The new_record attribute can be used to customize the button label.