Solution: delete metafields with data (second option) and then define the new datafield. 

Don't seem to be able to edit my post, so I am adding some additional info here. It is just to make it more clear. Above:Metafields have been renamed and are filled in. Product: Hydro+ InfinityBelow:The code snippet below references the old names  

Hello, On my website, I have changed some product metafield definitions (that is renamed the metafield, I am not talking about the associated content).  After having done that, the site appeared to work fine. BUT..I discovered I had forgotten to upda...