After some back and forth with tech support and our own ingenuity, we got the code to change the user's DBPASS credential in the CMS.  Here it is, if you're interested (note that "pennkey" is our University network user ID):

       //get session manager
       ISessionMgr sessionMgr = CrystalEnterprise.getSessionMgr();

       //get the session
       IEnterpriseSession enterpriseSession = sessionMgr.logon(boAdminLogin,
           boAdminPassword, boCmsName, "secEnterprise");

       IInfoStore iStore = 
(IInfoStore)enterpriseSession.getService("InfoStore");

       String query = "Select * from CI_SystemObjects " +
         "Where SI_Kind = 'User' and SI_Name = '" + userName + "'";

       IInfoObjects infoObjects = iStore.query(query);

       boolean hasResults = infoObjects != null;

       IInfoObject infoObject = null;

       //get results in a null safe way
       hasResults = hasResults ? infoObjects.size() > 0 : hasResults;

       infoObject = hasResults ? (IInfoObject)infoObjects.get(0) : null;

       hasResults = hasResults ? infoObject != null : hasResults;

       if (!hasResults) {
         log.log("There is no business objects user: " + userName, true);
         return;
       }

       IUser user = (IUser)infoObject;

       //db logon
       String dbLogon = user.getProfileString("DBUSER");
       log.log("DBUSER: " + dbLogon, true);

       //if dbLogon is there, make sure same as pennkey
       if (FastExternalUtils.isEmpty(dbLogon)) {
         log.log("Did not set the db password (no db username) for: " + 
userName, true);
         return;
       }

       user.removeSecondaryCredential("DBPASS");
       user.addSecondaryCredential("DBPASS", newPassword);

      //set username
       user.setProfileString("DBUSER", userName);

       //change the boPassword so we can login as that user
       user.setNewPassword(newPassword);

       iStore.commit(infoObjects);
       
       
====================================
Amy A. Miller, Senior Data Analyst
University of Pennsylvania ISC
Office of Data Administration
3401 Walnut, Suite 265C /6228
Philadelphia, PA  19104-6228
Phone: 215-898-2171 Fax:215-898-0386
Email: milleraa@isc.upenn.edu