From official XSI 2.01 documentation (Sue me !)
Beveling Polygon Mesh Components
The Modify > Poly. Mesh > Bevel Polygons command on the Model toolbar smooths corners by adding polygons. You can bevel polygons, points, and edges.
Beveling does not preserve texture projections. You should perform any beveling before you apply textures.
To bevel polygon mesh components
Select components on a polygon mesh object.
Choose Modify > Poly. Mesh > Bevel Component. The Bevel Op property editor opens.
Adjust the Bevel Ratio to get the desired effect. The maximum possible bevel depends on both the shape of the object and the selected components.