Ok
I extracted the esl files from the original gamecube version and I think I found the lines which make the Novistadors to appear in that room and they are identical to the esl lines from UHD port (just the bytes oder is different but they are the same numbers...) So, I guess the problem of those creatures not appearing in that room is more "hardcoded" than what I thought...
In case someone want to check it: I think the Novistadors code start in positions 1680 and 16a0 inside file Bio4\Etc\emleon03.esl
EDIT:
Hoho guess what I get! XD
Editing the esl file I managed to make the Novistadors to appear in room 20a again
It won't work if you play from chapter 3-2 or later savegame because the game (I guess) loads the spawn data from the game files at the beginning of every chapter (or room) and it keeps and stores that data in all following savegames.
Place this file (emleon03.esl):
mega.co.nz/#!tUhXmTZZ!kEtZw63TNugN3Xdzzbddi4wcsVnGYh1V5VoPV_WYTzQ
inside this folder "C:\Program Files (x86)\Steam\steamapps\common\Resident Evil 4\BIO4\Etc\"
and remove the original emleon03.esl.lfs
You can play from the end of chapter 3-1 (just before Ashley gets captured by the wall trap)