There is nothing wrong with the fact that the My Documents\BioWare\Dragon Age\packages\core\override folder is empty. Each mod has it's own requirement. you will have to check each mod's "readme" and/or description and follow the directions. Some may require you to extract the file or folders from within a "zip, rar or 7z file" meaning the files may be compressed into one file. and need to be "uncompressed" using a special and common associated decompression program (winzip,. winrar or 7z,) then inserted into override. You will have to then check with the mod creator themselves if you experience any difficulty with that particular mod.