Nobody else seems to have replied so I'll give it a go...
There is no ftp upload for images to iStock, but you can use
DeepMeta - indeed, that really is the best way in any case. That way you can copy and paste between similars and it will check at least the format for editorial uploads, which is critical on iS.
No, you can't change already uploaded ones to Editorial only; they will have to be re-uploaded. If you have a lot, use DeepMeta again - you can use its copy/paste facility to copy at least the keywords and stuff from the old ones to the new ones before adding the editorial caption.
I'm not sure how accepting they are of political candidate pictures - try one or two to start with and test the water. They are very touchy about locales, yes; I don't know if press credentials would be accepted. Best try support for that, or the Getty forum.
Best of luck....