Price List Validation

Dear Support,

I have a question regarding on the Price List of SAP B1 9.0,

if possible to have a script/validation on sales quotation unit price e.g on the price list table, Item01 has a value of 10,

now when i create a sales quotation

then i used that item (item01) then automatically  i have a value on my unit price equals to 10 . but now i am  trying to change that unit price and i want to make it lower.

then the validation trigger saying   "You can not change the value of unit price lower than the original."

can some give me and idea or a script to make it works..

Thank you

Regards

Silent,