After getting veneers can I get old teeth shape back?

Placing new veneers can return your teeth to their original size. It will be expensive and inconvenient for you, though. I would recommend you commit to your new smile for 6 months, save up for the new veneers and see how you feel. Often times big changes can make one feel like they aren't themselves anymore. If you stop worrying about it and try them out with an end in sight, you may find they fit your smile! Have your dentist save your original models. If after the six months you still dont like them, be sure to have a wax mock up of the new veneers made so you can see exactly what they look like on your teeth. It is a great way to see the changes and communicate to your dentist any changes you might want before they are made and bonded. 
Good luck!
Dr Ebnet

Hi:Depending on the position of the tooth and the reasoning for the veneers, you may be able to go back to the original shape.  For example if the tooth was sticking out too much and you wanted to have if more aligned with adjacent teeth, the tooth will be smaller once it is aligned.  Please post photos for a more accurate advice.Best,Dr. Maddahi