And you are also right in thinking that the only way to change the order of characters in this game is to dismiss your game-generated player characters in the next four slots is to dismiss them to the Adventurers' Guild and re-engage them in the order you want them to occupy.

The ability to change the order of your characters by highlighting one and Ctrl-clicking on another applies only to MM6. You can't do it in MM7. And the only game in which I know for certain character order matters is MM9. There, you can set the "formation" of your party - I think the keyboard command is either F or Ctrl-F, but I'm not certain of that. It's not well indexed in the manual.