Feature definitions are using feature symbologies that are using Element Templates that are using Levels.
Usually, only levels are part ot standards. Something that is probably evolving a lot but still it is the case in many places.
So what if you just want to change levels used by element templates ?
You can export element templates and run migration utilities to work in Excel.That is good but if you import the element templates it will rename them not replace them.If you delete the element templates then the feature symbologies are broken.
So we must find a way to replace levels without breaking anything.That is the trick (credit and many thanks to Chuck Lawson):
This process will force the levels to be updated while maintaining the linkages to the feature symbologies.