Trying to add an un-removable cursed Item (except via quest), and I don't want the loophole of being able to remove it by having it break? any way I can do this?

You could make it a clothing item with a shield enchantment.

That might work.
Second dumb question, how do I reference the *.nif and *.dds files without having to unpack everything? (or can I)

To do that you'd need the Custruction Kit Extender (thread http://www.gamesas.com/index.php?/topic/1250150-rel-construction-set-extender/) which will let you reference the content directly in the bsa's.

No need to create a script extender dependency for that.
if you mean adress direcly a vanilla mesh in the .bsa just create a directory in your data folder with the exact name of the one you want to use (eg clothes\lowerclass) and place a dumb file with the name of the cloth you want to use. Then in the cs choose this file. When done, delete the directory and he game will return to the default path (in the .bsa).

I did the reverse, changing all clothesin game to armor (so the NPC can remove them at night and wear only their basic undies to sleep ) using exactly this method. Same for the icon and the .gnd. You just have to copy/paste the model from the armor to the cloth model. Very simple and fast

Using the CSE doesn't create a script extender dependency, unless you use actual OBSE scripting functions.

Anyway, the game reads the .bsa naturally. There is no need for anything but the tescs to do something that simple, and there is nothing to unpack

Incorrect. You cannot use the basic CS to convert an armor item to clothing without unpacking the armor from the .bsa. That's why the CSE is needed in this instance.