Arihant,
1. Yes, but I would recommend not copying the old class, but extending the original Workorder and just overriding the required methods to keep things easy to follow and debug, and to avoid needing to change or extend other classes that refer to your POJO.
2. In the ERP config panel, look at the parameters for your application and modify the entry for group SAPOBJECT matching the class you want to change.
3. All your steplets should use the object factory to create the POJOs. This will automatically create your new class that you have now pointed to in the config panel. This is why you want to extend the original rather than copy it, because of all the other references. If you extend, the existing references will resolve correctly because your new object is still the same base type, only extended.
Jason Latko - Senior Product Developer at SAP