Some guilds are asked to testy high end raid content. For those tests the guild is copied over for a short amount of time.
The devs have already said they have no intention of allowing people to copy their characters over to test. They want individuals who are willing to actually test and try to find and report bugs and issues. They do not want to set up a system where people can copy their character over a few days before a live update just to see how their character is affected.