Hey, I need assistance with modeling. I have to displace some vertices and triangles from one TriShape (vanilla nif) to another one. In case to create separated TriShape. Is this possible to do in Nifscope? Or should I bother myself with import/export to Blender?

That will take Blender or Max to do, alas.

Right, but it depends on what you're really intending to do. Deleting a complete Trishape can be achieved in Nifskope. For more accurate operations, and as Madcat said, you need Blender or 3DS.