Sales Order Reason for change

Hello All

I have a requirement where we need to add order reason as a warning message whenever users makes following changes in the sales Order using VA02:

1. Change the Order Quantity

2. Change the delivery date for an item or items

3. Delete a particular line item

4. Add a particular line item

I know it can be handled via VA02 user exit. I have listed following user exits will be helpful:

USEREXIT_CHANGE_SALES_ORDER

USEREXIT_CHECK_VBAK

USEREXIT_CHECK_VBAP

USEREXIT_CHECK_VBEP

USEREXIT_CHECK_XVBAP_FOR_DELET

Can you please let me know out of these which one are apt for my requirement and also if let say user makes a change once in the sales order and maintains the order reason before saving it, but how will it be taken care for changes done by the user on some other time. Basically how multiple changes will be controlled?

Looking forward to your response.

Cheers

Ravi