Note: I don't recommend removing the bbdimension, Dimension zen, Dimension L, or dimension Today themes as some of the above themes need these in order to run. Also, 3rd party custom themes require these to be installed in order to function. Removing the Dimension themes will make it impossible to use these 3rd party themes.
If simply remove the cod files for these themes out of the Java folder, then simply moving them back will add them again. If you actually deleted those files, then you will need to reinstall the OS to your PC and start with your modifications again, making sure to leave those themes.
You can get the OS from blackberry.com. Just go to the downloads.