cd "C:\Program Files\Oracle\VirtualBox\"

VBoxManage.exe modifyvm "VM NAME" --cpuidset 00000001 000106e5 00100800 0098e3fd bfebfbff

VBoxManage setextradata "VM NAME" "VBoxInternal/Devices/efi/0/Config/DmiSystemProduct" "iMac19,3"

VBoxManage setextradata "VM NAME" "VBoxInternal/Devices/efi/0/Config/DmiSystemVersion" "1.0" 

VBoxManage setextradata "VM NAME" "VBoxInternal/Devices/efi/0/Config/DmiBoardProduct" "Iloveapple"

VBoxManage setextradata "VM NAME" "VBoxInternal/Devices/smc/0/Config/DeviceKey" "ourhardworkbythesewordsguardedpleasedontsteal(c)AppleComputerInc"

VBoxManage setextradata "VM NAME" "VBoxInternal/Devices/smc/0/Config/GetKeyFromRealSMC" 1

Also Add This Command only if you are using an AMD CPU.

VBoxManage modifyvm "VM NAME" --cpu-profile "Intel Core i7-6700K"

Other Valid CPU Profile:

Intel Xeon X5482 3.20GHz
Intel Core i7-2635QM
Intel Core i7-3960X
Intel Core i5-3570
Intel Core i7-5600U
Intel Core i5-4570