For some reason we wanted to change the default page of my site from example.com to example.com/default.aspx. We will be using 301 redirection to get the back link benefits. Do we need to make any changes in webmaster tool and sitemap too??
No, you don't need to change anything in webmaster tools, but if you have many links to old page then you will lose some link juice because of 301 redirect
If you are doing it because you are moving to a CMS, please check on forum related to that CMS. I once moved my site from static html to Joomla. It used to be PR3. The homepage fell from PR3 to PR0. It recovered in two months to PR2 and a year later was PR3 but came back to PR2 and remains there. Worse yet SERPs never recovered. My mistake was that I was not aware of 301 redirects then. Not sure if 301 redirect will take care of link juice