Anyway, just go to the template you want to copy, click Edit, then copy the entire source over here to the template page of the same name. So for example if the template you want to import is x, you go to Template:x, copy the source over to this Wiki, make a new page called Template:x, then paste code and publish.
It works the same way as Undo, except that if you rollback, you rollback the entire user's edits. For example, if a guy named Mike makes one edit, then a guy named Jamie makes one edit, then Mike makes 2 edits after Jamie, when you rollback, both of Mike's edits after Jamie's will be undone. However, Mike's edit before Jamie's will remain intact.
You could do so in Classic Editor (upload, then just undo the addition; the cache will be saved), but that's not too effective. I don't think there's any multi-upload platform, so you can only use Spezial:Upload