Problem with overriding validation of address

Hi,
I’m trying to make first name and last name in shipping address obligatory (as it is) and the same fields in billing address optional. I’m fighting with validation. I’ve created new validation group and assigned it to shipping address form and I removed all validation groups from billing address, but I cannot erase default validation of both forms. I figured out that this validation is related with file: vendor/sylius/sylius/src/Sylius/Bundle/CoreBundle/Resources/config/validation/Order.xml, if I remove those lines:
<property name="shippingAddress">
<constraint name="Valid" />
</property>
<property name="billingAddress">
<constraint name="Valid" />
</property>
everything if fine - form is validated only by new group. How can I override this file? I’ve try to make copy in src/Resources/CoreBundle/config/validation/Order.xml and change this file there, but it doesn’t give any effect.

Please give me some clue.