This message was posted on behalf of Intel Corporation
Regarding your question, “if there is a way to enable Hyper-threading without having to reboot the server“. I am afraid this is hard to say if you going to need or not a reboot for Hyper-Threading enabled. This because if the motherboard BIOS has the option Disable, then you will need to reboot the to enter the BIOS and enable it. If you get a BIOS update that will enable by default the Hyper-Threading, you still need to reboot for the changes to take effect. And depending on the OS, the Hyper-Threading enable settings, and you still will need to reboot for the Registry or Kernel to take full functionality on the changes.
Then I am afraid to say that yes you will need to reboot.
If there is anything else we can help please feel free to ask.