Changing default symbols bound to option key?
Create the folder ~/Library/KeyBindings/ and in it create a file called DefaultKeyBinding.dict and add whatever special character you need like so:

{
    "~c" = (insertText:, "⌘");
}


This makes ⌥+c insert the symbol ⌘. For more information on this file and its syntax refere to this article. After editing the file you need to restart your application for the changes to take effect.