The following procedure will default the CMC administrator password to null, but you'll have to re-import the biar file after you've completed this.
Excerpt from the BusinessObjects Deployment and Configuration Guide, which is attached to technical document.
Deleting and recreating the CMS database This procedure shows how to recreate (re-initialize) the current CMS database. By performing this task, you destroy all data that is already present in the database. This procedure is useful, for instance, if you have installed BusinessObjects Enterprise in a development environment for designing and testing your own, custom web applications. You can re-initialize the CMS database in your development environment every time you need to clear the system of all its data.
When you recreate the CMS database with the CCM, your existing license keys should be retained in the database. However, if you need to enter license keys again, log on to the CMC with the default Administrator account (which will have been reset to have no password). Go to the Authorization management area and enter your information on the License Keys tab.
Note: Remember that all data in your current CMS database will be destroyed if you follow this procedure. Consider backing up your current CMS database before beginning. If necessary, contact your database administrator. (this means you'll loose your biar file and any completed 'view my reports', which have already been requested, but you can reimport the biar and then re-request them so they're viewable again, once this is complete. However, please make sure you jot down the license key off of the CMC, home, licenses because you may need to re-enter it when this is complete)
To recreate the CMS database on Windows
While it is starting, the CMS writes required system data to the newly emptied data source. You may need to click the Refresh
The above procedure will default the administrator password to blank (null) no password.
After you login, you can reset the administrator password to what you like via the CMC, home, users.