Upgrading node Properties after module updated

[marcus-j-davies]

This topic keeps making an appearance.

Might be worth taking a read on this for some possible solutions :
I'm sure its relevance should help

How to change the name of a config field without breaking old flows

In a contrib node I need to change the name of a field. Can anyone suggest how I go about doing that such that config from old nodes is updated to use the new field name automatically? It is ok if the user has to open each old one and save it again, but I don't want him to lose the existing field contents. It is a dashboard 2 ui node (gauge classic) and I should have called the class field className so that the dashboard automatically picks it up.