@Pixy I
You want to change your forum posting name to "TheDarkKnight" but you can't as someone else is already using it, yet your posting name on the forum is "TheDarkKnight"
When you create your account on SOL, the system defaults your nickname to the left part of your email address. If it's already taken, like for example 'Jim', there are multiple accounts whose left part is jim@xx.xx. In this case, the system will add something to distinguish it. There is a list of suffixes and prefixes to do that. Mr_jim, Sir_jim, Big_jim, Jim_theMan, Jim_theLegend, etc...
After registration, if you want, you can change your nickname to anything, as long as it's not used by another account.
Now, when it comes to authors with stories, when posting, the system will give you a menu listing your nickname as the default followed by a list of your pen names. If you change your nickname to match one of your pen names, if available, then when you post using the nickname (default), then it will be treated as your identical pen name. Most pen names cannot be nicknames. Nicknames can't have a space in them, but pen names can.
The difference is, the poster's name in the forum, if it is a pen name (or identical nickname), it's linked to the pen name's stories page.
For a normal user, there is no clickable link, it's just the nickname.
And no, I won't change the system to highjack somebody's nickname if another person decides to use it as a pen name. Seniority matters in this regard, especially if it's something very common like 'TheDarkKnight'.
Of course, I'm aware of the possible confusion if the 'author' and the user with the identical nickname are different and they both participate in the forum, and the same thread. For example, the user whose nickname is thedarkknight, has been a paying member of the site since 2002.