Your original posts states that you want to delete the db_datareader role after assigning it's schema to DBA. Since it's a database fixed role, I'm not sure that you could delete it (I've not tried and probably won't because there's no reason to do such a thing) but, if you could delete it, I'm thinking that some seriously bad stuff is going to happen with your security because the system will check for the role while do other things (like normal login management, etc) and, when it can't find it, there will be forms of flying Kimchi that will make you cry out loud.
To summarize, don't even think of doing this
--Jeff Moden
Change is inevitable... Change for the better is not.