Welcome to the forum.
There should be no problem with some of those elements of Additional Functional Content, such as Titles (PRTL files), Menu Sets (mainly PSD's, but note that the PNG files are required to see the Menu Sets in the Library Display), and probably Transitions. I do not know about Themes/Instant Movies, but others should be able to help you here.
Were I adding Additional Functional Content to PrE 11, I would create folders (check out the necessary folder hierarchy, and duplicate that, renaming child folders, as necessary), so that the Library Displays include your added material. Also, some Menu Sets in PrE 10 had some issues, especially when adding an Image background. Those issues were fixed in PrE 11, do I would never replace any of the Additional Functional Content Assets in PrE 11, with any, regardless if the names match 100%, with Assets from PrE 10 - set up the folders for those additional Assets, so that they are separate, say in folders that have "PrE_10" in their name.
Hope that others have experimented with Themes/Instant Movies, and can tell you about those.