How to change default rendition from XML to a custom format?

Hi Guys,

I have created a content using content template that incorporates Rules file. Also, a .xls file for presentation purpose has been associated with the content. I have created a custom format (.cshtml) for the presentation that can be observed in the list of renditions available for the created content. But, whenever I try to open the content, it is shown in XML format (the format being the default rendition). I am not able to change this default rendition to .cshtml.

I have successfully opened the content in .cshtml format outside Documentum Administrator/Web Publisher i.e. by manually linking the XML file with the presentation file. But, I need to do it in DA/WP as I have to create Proof Of Concept(POC) in my project. Please help!

Reply awaited!