As Guillaume said, a template fallback is enough, in the sense that your new template will be used in every case. Teplate overrides are only used when specific conditions match.
In your new page_head.tpl you can fetch current object and get the attributes for meta tags, but that will be expensive in sql queries, ram and cpu.
So you should add a cache-block around that part (quick and dirty fix), or, better, rely on usage of the persistent variable (look up in the forums and tutorials on how to do it)
Principal Consultant International Business
Member of the Community Project Board
when you use the "attribute_view_gui" operator, eZ Publish call most suitable template file to display your attribute. If you want to know which template file is loaded for meta_keywords datatype, you can enable output debug and template output for your siteaccess. Then, you will see which template file is loaded in the source code of your page. This give you a lead to find why you have a line return in your code.
You can also decide to not use attribute_view_gui operator and modify your code to get this :
