After reading a part of RedHat documentation about SELinux, i think you need to restart the system ONLY if you made change while SELinux is disable. Then, you need to relabel your filesystem.
Actions made while SELinux is disabled may result in the file system no longer having the correct security context. That is, the security context defined by the policy. The best way to relabel the file system is to create the flag file /.autorelabel and reboot the machine. This causes the relabel to occur very early in the boot process, before any processes are running on the system. Using this procedure means that processes can not accidentally create files in the wrong context or start up in the wrong context.
It is possible to use the fixfiles relabel command prior to enabling SELinux to relabel the file system. This method is not recommended, however, because after it is complete, it is still possible to have processes potentially running on the system in the wrong context. These processes could create files that would also be in the wrong context.