It seems that you can edit Quest games after they've been published, but can the same be done for Squiffy games? Because I want to make a story that comes out in separate parts but are still included in the same game, and I wanted to know if I could do that or if I would have to have completed them all before I can do that.

No, it's easy to add to a squiffy game. Roughly, here's the process.

Under the "Create" top pulldown, click on "create". This should take you to a page with two big green buttons (for creating Quest and Squiffy game). Ignore them. Beneath them are two tabs, one of them for listing your Published Games. Click on that.

Select the game you've published. You should see a View/Edit hot link. Click there.

Now you are in your game page. There should be two blue buttons, one for changing the listing, one for the picture. Listing will allow you to reload in a new version of your game. For my updates (and I'd done it possibly a hundred times) I need to...

1. Reload the game
2. Change the description (i.e. new version numbers and information for my description field
3. New game image. Reloading a new game wipes this out and you have to replace it.

Hope that helps.