I'd say that if you go about a month and are not getting a lot of surveys, you could change one time to a different person with a different email address. I wouldn't switch it more than once a month. But if one of you gets tired after a while or are not getting a lot of surveys, they should not get mad if you just change it once. Now, if you change and that person isn't getting any, you will be stuck because you won't be able to change it back again.