I have both CS 5.5 and CS 6 installed with 5.5 versions set as default. Illustrator had issues opening the wrong version so I found how to set the default in the registry. Now it works correctly, double-clicking opens Illustrator 5.5 and if I right-click, 'Open with' has an arrow with 3 options, Illust CS5.1, Illus CS6 and Choose default program...
How can I get Indesign to work the same way? For Illustrator, the registry key is under HKEY_CLASSES_ROOT -> APPLICATIONS -> "your application" -> shell -> open -> command but for InDesign, there is no such key under applications. I did find under " HKEY_CLASSES_ROOT -> InDesign.Document>Shell>Open>Command>Default" which did not have a value in the key. When I added the path to Indesign 5.5 there it did not work. The path merely showed up in the right-click contextual menu at the top but "Open with" had no arrow.
I have attached screen shots showing the different behavior between Illustrator (correct) and InDesign (not working as desired).
Even when I try to set the InDesign CS6 as default temporarily, only 5.5 shows up and if you browse you can select CS6 and click OK but it does not show up in the default window.
In my experience, it makes no difference what you tell Windows to use, it will always open the last installed version of InDesign.
I did successfully get both Indesign and Illustrator to open the CS5.5 versions when you double click (default setting for me). I would just like the option to have Indesign give me a choice when I right click so I can occasionally use CS6, just like Illustrator is doing now.