So, i'm currently trying to edit the .nif for the "tuxedo hat" (specifically, trying to move it lower on the wearer's head), but nothing I do in NifSkope has any effect ingame, or in the GECK preview. I've tried creating a new item and using the edited mesh for that, but no, still looks exactly the same, even if i flip it upside down and move it way off to the side in NifSkope, the only change I see ingame is that the texture has changed to flat black... anyone able to help? is there some extra step that i'm missing beyond changing the translation settings?

Anyone? Help?

After altering the transforms, you'll need to apply them. (rClick the TriShape and do Transform>Apply). Sounds like it's being ignored in this case.
After that, you'll need to export the 'new' hat as an obj file from NifSkope, and run that through the Conformulator to generate an .egm file.