You can now convert legacy single-page apps to multipage without needing to leave the IDE. Navigate to the Pages tab, and click Convert to multipage.
If you change your mind and want to undo this change, navigate to the Releases and history Releases and history tab and revert your app to the change before the Migrated app to multipage change.
The last time I tried to migrate an app and import the previously separate apps I had created, instead of merging redundant queries, it created copies, which I then had to spend a lot of time cleaning up. Is there a way to import apps and have it ask if you want a query to be merged or duplicated?