programmatically set extra fields value

-- HikaShop version -- : 4.5.0
-- Joomla version -- : 3.10.6
-- PHP version -- : 7.4.3
-- Browser(s) name and version -- : Chrome 90.0.4430.212

Hello,
is there the possibility to set the value for extra fields programmatically via php?

I have managed extra fields for order, and i want to set their value on checkout page based on the user logged in. Those data are stored for user in a third party backend.

Thank you

thank you,
the goal is to set value to custom fields (order table) while they are shown in checkout page (show_block_fields)
is it possibile?

with your code i think the value is set only after user click "Confrm button" on checkout page, but my custom fields are shown in that page and i want to set a default value for they, and let user change it if he wants to.

thank you

ok thank you
i tried to create a plugin w/ group "hikashop" implementing JPlugin with:

function onAfterCartProductsLoad(&$cart) {
$cart->cart_fields->xxx = 'yyy';
}

but it is never invoked! am I wrong?

thanks

ok i manage to resolve my problem!
thank you very much for support