After the shipment of the robot are we allowed to add other parts. 
No, you must send all parts that are to be used on the robot with the robot. The only exeption to this is that you may keep the OI to play with the EduRobot after shipment.
The previous answer was a little misleading…
First, let’s get this simple rule straight: All robot components must be fabricated within the 6 week build period.
Now, you can build components at the competition (regional/championship) and put them on your robot. That is certainly legal. Last year they let us build ‘spare parts’ for 3 days after the competitions.
Technically, there’s nobody keeping an eye on you. It’s up to the teams to use ‘good faith’ and ‘gracious professionalism’ and not cheat by making parts outside of the alotted timeframe.
Please note that team update 15 will address this issue. Until that point we really don’t know what FIRST will allow, THIS YEAR, we can only let you know what has been allowed in previous years.
Here is more information about this year: http://jive.ilearning.com/thread.jsp?forum=3&thread=1694&message=4197