Additional filtering on a variable

Hi all,

for example I have a "Stores" characteristic that I'd like to restrict in my query, for user to choose one of all the stores.

But I also have an "Active Flag" attribute, and, for example, I'd like user to see when choosing the value of the variable only the stores that have the value of that attribute equals to "1".

How can that be done?

I believe there should be a customer exit involved. But how do I do that?

Best regards,

Andrey