The goal of this file is to have a place to easily commit answers to questions in a way that's easily searchable, and can make its way into official documentation later.
This is a supported operation. Today, the MCO does not have good support for "per node" configuration, and configuring things like static IP addresses and partition layouts by customizing the Ignition makes sense.
However, it's important to understand that these custom changes are "invisible" to the
MCO today - they won't show up in oc get machineconfig. And hence it's not
as straightforward to make any "day 2" changes to them.
In the future, it's likely the MCO will gain better support for per-node configuration as well as tools to more easily manipulate Ignition, so there is less need to edit the Ignition JSON directly.
Today, the MCO only blocks on upgrades of control plane nodes. oc get clusterversion effectively reports the version of the control plane.
To watch rollout of worker nodes, you should look at oc describe machineconfigpool/worker (as well as other custom pools, if any).