Edit the task sequence to update settings in the steps that you want to use, to add steps, or to delete any steps that you do not need.
Client script
Clearing the PXE advertisement allows the machine to boot into PXE once it does reboot. If this is not done, the machine might reboot, but Configuration Manager will not offer PXE boot to the machine.
Setting the PxeRebootStep machine variable allows the task sequence to branch off and perform only specific actions based on conditions set in the task sequence on groups or steps.
There is nothing required for you to do with the client script, and you should not edit the client script.