Are you able to edit quest games that were created in the Quest Program you download in the online version?

From what I can see, this isn't possible, but I just wanted to make sure.

yes, you can. If there is the download button you can download a game.zip. Within you will find 2 aslx files of your game but you can ignore the backup file

oh okay,
does it work the other way around as well?

No, there is no facility for sending a file back to online to be edited.

You can upload the published Quest file to be played when you're done creating it with the desktop version, so you're able to still have it played online.