I think it's not useful. It will be used at least by 1% of translators. Currently you can download langpack, modify it with any editor wich supports multifile replace, zip modified langpack, upload it back.
One russian contributors member created script, that makes replacements with sed utility - it can make complex replacements, like changing 'x' quotes to <<x>>. Pity, i have no time to fully test and use it ...