Unless you have some refactoring tool that does support this type of modification, you can't really add it directly, except manually. There are plans to add support for Legacy settings in release d, that would help in this scenario, but it hasn't been implemented yet, so it will not help either.
What comes to mind is to create a class, CustomToolbar, that will inherit from ToolBar and in the constructor call the base's constructor and then set the TextAligh property to Right. Then you would need to do a global scan/replace on your project, replacing Gizmox.WebGUI.Forms.Toolbar to your CustomToolbar type, making sure it will not replace for instance "Gizmox.WebGUI.Forms.ToolBarButton" in the process.
Hope this helps,