Refer to Noire's main.xml for MC12 specific differences but basically, to quickly upgrade an existing MC11 Theater View skin, do these things to the skin's main.xml:-
1. Increase the MJFS version to 2.0, eg> <MJFS version="2.0"> --- this alone will get things up and running.
2. Add this block to the file (required for MC12's new seach function):
<SEARCH>
<Text TextColor="FFFFFF" SelectedTextColor="FFFFFF"/>
<LetterBackground Bitmap="Search\LetterBackground.png" Columns="10,?-Flex,10" Rows="10,?-Flex,10" InternalMargins="6,6,6,6"/>
</SEARCH>
Note: You'll need to copy Noire's "Search" folder for the LetterBackground.png file into your skin's root directory.
3. Finally, MC12 supports different backgrounds for different view levels. To use the same one everywhere, make the <background> block look like this:-
<BACKGROUND>
<Item Location="*" Bitmap="<backgroundFile>"/>
<Item Location="*\***" Bitmap="<backgroundFile>"/>
</BACKGROUND>
... where "<backgroundFile>" is YOUR chosen bitmap file. For example, "Background.png".
Hope this helps.