Adding extra strings to Lang file from within game

So I have a dictionary to store all my strings from in a plugin, and I need to add strings to that file from within the game.
I have been re-registering the langfile after the user has entered their string which works, but the problem with that was once the plugin restarts it removes all the extra strings. I had come up with a dodgey way to get around this but now it turns out on server restart it just removes the strings again.

Is there anyway to add these strings without it automatically removing them on server restart/plugin load?

It's this piece of code from the function MergeMessages in Lang.cs

Code:

 // check for old keys
            foreach (var message in existingMessages.Keys.ToArray())
            {
                if (!messages.ContainsKey(message))
                {
                    existingMessages.Remove(message);
                    changed = true;
                }
            }

@Wulf this is in regards to KillStreaks