Update Scenario of Discount Rules

Hello,

How to update the already created Discount Rule? There is ChangeType=UPD which we are rying to use. But DIMP message corresponding to Discount Rule has a Rule ID which does not map to Primary Key of table RU_PRDV. It maps to ID_PRM column which is not part of Primary Key.

So, how Update works when we can not pass primary key related value for discount rules.

Thanks,

Nilesh