Conditional privilege

Hi,

I need a conditional privilege in Xstore and I don't see how I can do this.

The Xstore privilege CHANGE_PRICE should be conditional.

In case there is a regular price, then the normal privilege should apply.

But in case there was no price found in the database (in that case Xstore returns 0,00 or -0,01) then the privilege should not apply and everyone should be able to change the price (1 or more times during the transaction)

I tried to remove the privilege from the ACTION and added an extra operation to trigger the privilege, but I do not succeed.