GeoMesh allows you to modify an existing mesh or create one from scratch.
You can translate, rotate, scale selected points and faces, add or delete points and faces, and duplicate a selection. You can also create a mesh from scratch by writing a list of coordinates, and conversely you can turn a mesh into a list of coordinates.
Here is the GeoMesh documentation.
How to install GeoMesh?
Download this archive, unzip it and put it in your .nuke folder.
Then add these lines to the menu.py file:
import geomesh
nuke.menu('Nodes').addCommand('3D/3D/Modify/GeoMesh','geomesh.new()', icon=geomesh._icon)
nuke.addOnScriptSave(geomesh.save_all)