Use a different User Name. Each user name can only play an island (or part of an island) once.
you cant
no, you don't.
The Pandora app can play a song more than once in the same day.
Unfortunatley, you can only do each island once. To do it again, make another character. There is no limit on how many characters you can have.
it plays automatically
You can replay an island by going on the small island map (upper right) and pressing the "restart island" button on the bottom left corner. A player (same username) cannot earn more credits for an island once it has been beaten.
if you want to play it more than once you have to download it
Yes
Yes. However, the ending sequence may not let you play again once you win. If this happens, you can restart the island from the small map at upper right. You will keep the Medallion and credits, as you cannot win them more than once.
yes you can always play it if you unlock it!
Yes. Beginning in 2010, an island could be reset to play again. Click the small map at upper right and there is a blue button to restart. You cannot earn credits for any island more than once for any username. (see the related question)
In order to play the island again for credit, you can create a new username and avatar. But you cannot combine credits among your usernames. Any time you are playing an island, even after you have beaten it, you can restart play by selecting the small island map and clicking "Restart Island." This will erase all items and place you back at the starting point. However, you cannot earn more credits (on the same username) for an island you have previously completed. On your status page (star), the Medallion will not actually disappear if you restart an island that you have completed.