Thanks for your reply, Chris. Your suggestion of using an underscore will work, although an underscore is an acceptable character in an Ancestry DNA username, so this could potentially cause some confusion with some people's usernames.
The other thing I've noticed is there are lots of Ancestry DNA kits that are administered by relatives. These kits appear as the initials of the test taker, followed by "(administered by [username of administrator])". The Ancestry DNA username field here on WikiTree is currently too small to allow all of this to be entered. Because of the large number of Ancestry DNA test takers with the same initials, the administered by part is necessary to differentiate between tests. I'm hoping the Ancestry DNA username field here could be expanded to accomodate this. I don't, however, know what the specific character limit of Ancestry DNA usernames is.
Hope this helps.