This might be a ASP.Net master page question, But I have couple of content place holders defined in master page.  Like :

<CPH1>

<CPH2>

</CPH2>

<CPH3>

</CPH3>

</CPH1>

This CPH1 is override in child pages (not all). I have 3 sets of child

1) Replace their own content by adding a blank CPH1

2) Partially replace content by replacing a blank CPH2

3) Does nothing and inherit all from Master.

In my existing template which had blank CPH1, I want to inherit partially from Master. If I remove the declaration of CPH1 from child template it gives error. I have not get error details but will capture later. I have loads of published pages using this template. I tries republish the complete site.