View the original community article here
Last tested: May 18, 2020
You can move the explore into the new model, and those looks will start erroring. Then you can change the model on those looks (since the explore will be erroring, but you can change something besides what is erroring).
If a group of looks all have the same error, you can change them all at once.
There is a feature request for allowing content validator to work on some subset of Looks.