If you are not using the approval process stopping a deliver from happening will be very difficult, as the portal request is handled in the following (high level) manner:
- User makes the request on the portal by clicking on the Request button
- Server receives the request from the client computer
- Request is parsed to get the requested software and computer details
- A clone of the SWD Policy is made and assigned to run asap on the requestor's computer
- Server sends a response (page) containing code to force a client confi request on the computer
- Altiris Agent makes the request adn receives the new policy
- Requested software is now installing
As you can see it all happens very fast, so there's next to no room for human intervention.