You can make a nLite addon for this to insert the registry entry into install media registry.
1. Make a file called Entries_POSReady.ini and put in the following contents
;=======================================
; Entries_POSReady nLite Addon Registry Keys
;=======================================
[general]
builddate=2019/11/10
description=Entries_POSReady
language=English
title=Entries_POSReady
version=1.0
website=
[registry_addreg]
HKLM, "SYSTEM\CurrentControlSet\Control\WindowsEmbedded\ProductVersion", "FeaturePackVersion", 0x0, "SP3"
HKLM, "SYSTEM\WPA\PosReady", "Installed", 0x10001, 0x1
2. Zip the file into POSReady_Regtweaks.zip
3. Add the zip file as addon into nLite