Just to make sure we're on the same page here, can you please confirm that what you're trying to do is access the custom filed for your blog posts through code, is that correct? If so, you can get the value of the custom fields in the codebehind, using the extension method GetValue (please add a reference to Telerik.Sitefinity.Model in your class):
YourProperty = DataExtensions.GetValue(currentItem,
where YourProperty is the name of the public property, currentItem is the current BlogPost item and "CustomFieldName" is the name of the CustomField that you added.
If this is not the case, please send me your template, so I can get a better understanding of what you are trying to achieve.
the Telerik team
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