The Customize item is missing from Workspace drop down menu list in MicroStation V8i (SELECTseries 3).
Customize dialog still can be opened running Key-in: Customize Dialog
Some changes were done in ..\Workspace\System\GUI\GUI.dgnlib file. If the custom Workspace or from older MicroStation version Workspace is used such issue may appear.
Copy/replace the GUI.dgnlib file from the delivered MicroStation V8i (SELECTseries 3) – 08.11.09.357 or08.11.09.459 Workspace in your custom Workspace.
By default in Windows 7 OS MicroStation Workspace is located in: C:\ProgramData\Bentley\MicroStation V8i (SELECTseries)\WorkSpace\System\GUI\