In your master page's page title, enter the macro:
{% if(CurrentDocument.ClassName == "your.classname"){DocumentName + " - " + CustomFieldName}else{DocumentName} |(identity)GlobalAdministrator%}
This macro will recuse through the rest of the content tree. So this is assuming you have NOT added the CustomFieldName
to every page type you use in your site. It checks to see if it is the class name you want and adds the field value to the document name. This is a "set one time and leave it" functionality.