Explanation
The updated policy is serially applied to the virtual machines is the correct answer because changing the rule in the assigned policy will trigger a policy compliance check and a resynchronization of the affected objects.
The policy change will not be rejected, queued, or ignored, as it is a valid and supported operation. However, the policy change will not be applied in parallel, as that would cause too much network and disk traffic.
Instead, the policy change will be applied one virtual machine at a time, starting with the most critical ones, until all virtual machines are compliant with the new policy. References:
VMware vSAN Specialist v2 Exam Preparation Guide, page 9