Ok, so without either a dev that wants to write custom unpacker/repacker or buying UnityEx paid version you won't do anything.
All important files seems to be stored inside UnityFS compressed bundles (there is no big unity3d at least). This was made by Unity 2019.4.24f1, but UnityEx for some reason treats it as 2020. Both are hidden behind paywall, so result is the same.
I don't know about any tool except for UnityEx paid versions that supports their bundles and allows for unpacking and repacking stuff.
Versions before paid version was introduced throw error when trying to read bundles from this game.
