The documentation says that the IMDSv2 can be enabled for existing machines by editing the machineset. However, this only actually works for new machines and not for exsting machines. If the machineset is scaled to create new machines, the new machines come up with the IMDSv2 enabled but the setting doesn't change for the existing machines.

Doc: https://docs.openshift.com/container-platform/4.15/machine_management/creating_machinesets/creating-machineset-aws.html#machineset-imds-options_creating-machineset-aws