Not afaik, you can do it by installing windows in a VM in audit mode and let WU install them or download the definitions exe and install it manually in audit mode, sysprep and capture the install to a wim. Or install the definitions exe by setupcomple.cmd. I don't get why you want it, by the time you install the iso, there will be new definitions available on WU.
Code: Start /wait %systemroot%\setup\scripts\mpas-feX64.exe /Q Should be enough, don't forget to include code to selfdelete the setupcomplete.cmd and scripts folder after it ran.
with every day new updates for defender I would say it is a waste of energy and time so good luck with this and I hope you find a way
Offline updates via MMPC (Microsoft Malware Protection Center, now renamed to whatever) can be integrated as stated by the others above, but it's really a futile exercise: Cloud-based definitions are exclusively served via Windows Update and are always one, two steps ahead, superseding the offline (manual) ones. 10 out of 10 times. Even if you just made the ISO. Plus, Windows will force an update after setup by design (actually, two with the product rebase one), even if you manage to integrate the very same definitions build. And before you ask about it, no, Cloud-based definitions are not made available like the other updates.