You can already (so I guess I'm misreading your request).

To share .prc files, add its extension to the list in the Options->Sharing->Shared Extensions (use a semi-colon to separate extenion types)

To block an extension, add it to the Options->Filters->Keywords

or, when the results come in, use the Tpye Filter panel on the Search Tab to just show the .mpg (or whatever) results