Hi,
Thanks for your response. That lead me to the right direction 
I tried adding that in manual section considering the default section are also added. But I got this error
Windows could not parse or process unattend answerfile [C"\windows\Panther\unattend.xml] for pass (specialize). The answer file is invalid
I just figure out that the issue was due to the fact that I’m doing the PXEboot on a virtual machine and the chassis type won’t work for that virtual test machine I had.
Thank you so much!
[Init]
ComputerSerialNumber=#Right("%SerialNumber%",7)#
[ByLaptop]
Subsection=Laptop-%IsLaptop%
[ByDesktop]
Subsection=Desktop-%IsDesktop%
[ByVirtual]
Subsection=Virtual-%IsVM%
[Laptop-True]
TypeCode=Laptop
OSDComputerName=%TypeCode%-%ComputerSerialNumber%
[Desktop-True]
TypeCode=Desktop
OSDComputerName=%TypeCode%-%ComputerSerialNumber%
[Virtual-True]
TypeCode=Virtual
OSDComputerName=%TypeCode%-TEST
[Settings]
Priority=Init, ByLaptop, ByDesktop, ByVirtual, Default
Properties=OSDPREFIX, BFClientVersion, BFClientFileName, ComputerSerialNumber, TypeCode