Does this question refer to Hadoop Service Level Authorization?
http://hadoop.apache.org/docs/r2.7.1/hadoop-project-dist/hadoop-common/ServiceLevelAuth.html
If so, then there is no need to restart the NameNode to make changes in service-level ACLs take effect. Instead, an admin can run this command:
hdfs dfsadmin -refreshServiceAcl
More documentation on this command is available here:
http://hadoop.apache.org/docs/r2.7.1/hadoop-project-dist/hadoop-hdfs/HDFSCommands.html#dfsadmin
There is similar functionality for YARN too:
http://hadoop.apache.org/docs/r2.7.1/hadoop-yarn/hadoop-yarn-site/YarnCommands.html#rmadmin
Another way to manage this is to declare a single "hadoopaccess" group for use in the service-level ACL definitions. Whenever a new set of users needs access, they would be added to this group. This shifts the management effort to an AD/LDAP administrator. Different IT shops would likely make a different trade-off between managing it that way or managing it in the service-level authorization policy files. Both approaches are valid, and it depends on the operator's preference.