Hi Kalyan,
The first part of your question, can be the flexibility given to use this date field as per need.
Such are many instances.
Coming to How to restrict?
1. This can be by changing attribute of system messages to 'E'. But I feel option below is better.
2. User-Exit way.
For Notification: QQMA0014
For Order:IWO10004
Jogeswara Rao K