So the short answer is that files in the TNormal folder will overwrite files in the TLowRes folder.
IIRC, and you can check this, the three files should actually be all the same, just with different names.
So you take druck_radio_7, copy it and rename it to druck_radio_9 and druck_radio_21, and they all should work. Just put them in TNormal. I'd say leave the ones in TLowRes to make sure that the overwriting files work. It will be easier to tell, because then you can tell if something is going wrong.
Ultimately, if you have some image editing software, like GIMP, you could open the file and put any poster in there you want. Just paste it fully in the slot where the poster is in the actual file. Depending on how editing software savvy you are, you could, for instance, put a pic of your nephew with a captain's hat on in there.
You can't really mess it up.
Good luck!
