RT Custom Field validation

Is there a way for Custom fields to have a validation on creating a
ticket? Like have the validation cross reference the data that was
inputted in the field to the value that was setup for the custom field.
I have a custom field that has select or type the value of a Store # and
I want RT to validate if that store # inputted exist in the values name
list on the backend. Anybody know of a script or extension that can do
this?

Thanks,

Michael Neuschafer

PC Support Specialist

National Stores Inc.