How to make Flash galleries show more than 500 pictures?

You need to modify the Flash template. This is at

Windows: C:\Program Files\Adobe\Adobe Photoshop Lightroom 4.x\Shared\webengines\default_flash.lrwebengine
Mac: Applications\Adobe\Adobe Photoshop Lightroom [version]\Shared\webengines\default_flash.lrwebengine

Copy that lrwebengine to

Windows: C:\Users[user]\AppData\Roaming\Adobe\LightroomWeb Galleries
Mac: [user]\Library\Application Support\Adobe\LightroomWeb Galleries

Open the file galleryInfo.lrweb in a text editor. Notepad is fine on Windows, or TextEdit on Mac where you may need to right click the lrwebengine and select “Show Package Contents” to get to the file itself.

Look at line 21 and replace the following lines with this:

title = LOC “$$$/WPG/Templates/Flash/Bluefire1=Lightroom Flash Gallery > 500”,

id = “com.adobe.wpg.flash.bluefire1modified”,

galleryType = “Flash”,

groupPath = “resources/mediaGroupData/group.xml”,

mainSWF = “resources/gallery.swf”,

maximumGallerySize = 50000,