But this only works for "flat" properties (like myProp in previsous example). If I add properties including nodes (e.g. subnode/myProp) then the break inheritance icon is shown, but when you break the inheritance, change the value in the livecopy and start a rollout again then the changed value gets overwritten although the dialog shows that the inheritance is broken.
If the content volume is minimal, you can consider changing the property name. In which case, approach would be
Back up old content -> Prepare migration script for already authored content to get updated to new property path(should be a copy action rather than move to support old path till we update the property name. Later when things are fine, you can purge old property path) -> then change the property name (Should be fine for future content as well as for already authored pages)
If it is huge and can't risk about existing content, consider the above workaround from the blog post.
Note : Either ways, content backup is super important for scenarios like this in each environment.