How to customize the pages section in admin side of SilverStripe?

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Question:

I want to consider a flag for pages which are defined on the admin side and load them based on this flag (I mean I want to load them if this flag is true), and also I want to load the rest of them in the separated section of the admin. I’ve added the flag in advance to related DataObject, but I have no idea how I can change its fetching DataObject methods.

Could you please help me to handle it?