This cannot really be done, because the plus sign represents a space in a URL, and that is different from a hyphen. In other words, the tags "user profile" and "user-profile" are technically different. Same thing with usernames.
You could switch back to using space-separated tags, so that tags use hyphens and not spaces. But based on your other question I think you probably don't want that.
But I don't think there is any problem, there is nothing wrong with using the +