You can add your own custom attributes for UML static structure using Visio in the following way.
1.On the File menu, point to new, point to Software, and then click UML Model Diagram.
2.In the tree view, right-click the package in which you want to include the static structure diagram, point to New, and click Static Structure Diagram.
3.Drag class or object shapes onto the drawing page to represent the classes or objects you want to include in your class static structure diagram or conceptual model.
4.Double-click each shape to open its UML Properties dialog box, where you can add attributes, operations, and other properties.
www.office.microsoft.com/en-us/visio-help/create-a-uml-static-structure-diagram-HP001208873.aspx