Hi!
 Could give a precise definition of what you mean by stellation?
 There is a quick reference page about things you can do with a polyhedron:
 https://doc.sagemath.org/html/en/them...
 Perhaps what you mean is related to the following methods. Say P is a polyhedron object then
  - P.barycentric_subdivision(): constructs a polyhedron out of- Pwhose facets correspond to complete flags of faces of- P.
- P.stack(face): puts a new vertex a little bit outside of the face- face.
In general, Sage tries to follow the nomenclature presented in the Handbook of Discrete and Computational Geometry (Chapter 15):
 https://www.csun.edu/~ctoth/Handbook/...
 Is the operation described in there?
 Otherwise, please let us know what is the operation and we will add it to the desired methods.