Hi Aditya,
what kind of extensions are we talking about? If you've uploaded buttons/icons to show menus or similar stuff, you can customize features of Cognos roles.
E.g. we use the CogBox and an extension we've created called the "Quickstarter". For some roles, the CogBox extension is not visible (Manage/People/Accounts/Cognos/<your role>/Properties/Customization/Features.
Pick the view where the extension doesn't have to show up and uncheck the box next to it:

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Robert Dostal
Team Leader BI
GEMÜ
Ingelfingen
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