You can access the page Meta tags by iterating through the HeaderControls collection of the cmspage object.
For each HeaderControl object in the collection you can invoke LoadControl()
method to get the System.Web.
UI.Control object. For the Header controls, the returned type could be System.Web.UI.HtmlControls.HtmlMeta, System.Web.UI.HtmlControls.HtmlLink or System.Web.UI.HtmlControls.HtmlGenericControl. Then you can access the Attributes collection of the returned from LoadControl() HtmlControl object.
Another approach is to access directly Attributes collection of the HeaderControl.
If you intend to change HtmlControl data, i.e. properties, attributes, etc. you have to join the HeaderControl object into a transaction first, and finally when you want to apply changes, you have to Commit the transaction.
But the above solution will be obsolete in the upcoming release of Sitefinity, because the API of the CMS module has been changed regarding Partially Trusted support implementation and some improvements.
So, here is an approach which you should use in the Sitefinity RC2, for example adding a head tag to a page: CmsManager manager = new CmsManager();
bool forEdit = true;
IPage page = manager.GetPage(pageId, forEdit);
HtmlMeta meta = new HtmlMeta();
Hope this will help.
All the best,