Creo Direct > Designing in the Creo Direct Environment > Working in Part Mode > Working with 3D Geometry > Editing 3D Geometry > Substituting Faces > About Substituting Geometric Entities
  
About Substituting Geometric Entities
You can substitute or replace geometric entities such as surfaces or faces with existing quilts or surfaces in a model. Any round geometry between the substituted surface and the model is recreated after the substituted geometry is attached. When substituting geometric entities keep in mind the following points:
All the surfaces in the geometry selection must belong either to the solid geometry or to the same quilt.
The geometry selection must be nontangent to the neighboring geometry or must be attached to it along with the round geometry.
The substituting surfaces must be large enough to attach to the neighboring geometry without the need to extend them.