Thank you for your feedback.
I don't need to make any web domain config change.
I tried updating without any domain_record parameter set, just to get the vhost config to be generated again against the new template.
But then my update action gets ignored.
Also tried just setting a parameter without actually changing it;
$domain_record['active'] = 'y';
but this gets ignored too.
Is there a way to work around this without having to update/change a parameter temporarily?