You can consult or modify a DBMS definition file using the Resource Editor. When you select a category or an item in the left-hand pane, the name, value, and related comment appear in the right side of the dialog box.
You should never modify the DBMS files shipped with PowerDesigner. You should instead copy the DBMS to create a new one. To do so, create a new DBMS from the List of DBMS, define a name, and then select the original file in the Copy From list.
For more information on using the editor, see Opening Resource Files in the Editor.