Add New Intsrument(s)

Is there any way to add another instrument (s) to a score once it is finished? It seems you cannot go back to where you originally set up the New Score, and add instruments to the list. I want to add a Bass Guitar to a Rock Song, Or maybe, one could start a New Score, and Copy and Paste the already finished old score into it, having added the new instrument in the new score area? Please see attachment.