Abhishek,
You can add request or response data protocols handler (DPH) after the Virtual Service Model is created, but not after the VSM is deployed to the VSE.
To add a request DPH after the VS is created, you need to go the Listener step, select Filters, select the plus icon , select the Virtual Service Environment option and Data Protocol Filter. You will have access to all the DPHs available during the recording process.
When adding the DPH during the VS creation, you will be able to see the request information and edit accordingly, if needed. If you add the DPH after the VS is already created, you won't be able to see the request or response details.
Heloisa