By using wimboot from the iPXE project it is possible to directly MBR-boot to grub4dos or grub2 from a USB drive and install Windows onto a target system by just using unmodified Windows install ISOs.
It is also possible to specify any unattend.xml you wish (optional).
Instead of running Setup.exe as shown in the examples, you could use WinNTSetup or DISM or some other method without needing to modify the ISO.
Follow my blog post here to Tutorial 145 for more details.
Edited by steve6375, 3 weeks ago.