You can exceed the server 5 slot character limit, up to a maximum of 10. If you try to go beyond this you get an error and the game crashes to desktop.
It's fairly easy to replicate via the below:
Switch to a server with open character slots
Switch back to your main server
Mash 'create character' as the server transition occurs
If done right you will be on the character creation screen which upon completing adds the new character to your main server.
It's mostly useless as once you exceed the 5th slot it starts replacing and removing characters in the list, meaning you can no longer play some/all of your original 5 characters. When you have filled all 10 slots there is only one character choice (the 6th character created) available for playing with.
