I am working with clearQuest 7.1.2. I have two question in clearQuest 7.1.2 ..
1- There are no specific API for update Group and User in ClearQuest, CMAPI only provide setter method for both object's attributes. If we use those provided setter method to modify the attribute it will overwrite its value, if you don't want to overwrite you have to write code in that way.
2- No there is no 64 bit ClearQuest installation available . see this link - http://www-01.ibm.com/support/docview.wss?uid=swg21330262