You can define VB .NET preprocessing symbols and values in the preprocessing tab of the reverse engineering dialog box.
Symbol names are not case sensitive but they must be unique. Make sure you do not type reserved words like true, false, if, do and so on. You must always assign a value to a symbol, this value can be a string (no " " required), a numeric value, a boolean value or Nothing.
The list of symbols is saved in the model and will be reused when you synchronize your model with existing code using the Synchronize with Generated Files command.
For more information on the Synchronize with Generated Files command see Synchronizing a Model with Generated Files.
You can use the Set As Default button to save the list of symbols in the registry.