If I understand your issue, you have say 100 servers, 98 with the admin account of say joe.bmc and the other two with different admin accounts, say fred.bloggs. You have one role that you want to use to manage all of the servers but in that role you have map as user joe.bmc ?
Create a server property of Admin_account with the default setting to be joe.bmc, then on the two servers where you need a different account change the property to be fred.bloggs.
In the role map to the server property not to the named user, Admin_Account, when the ACL push job runs it will populate the users file with the value in the property. You can preview it by just running an ACL push to a single server, before the push occurs you are presented with a preview of the file that will be pushed.
In the role setup you can map to a property not a user.