Are these new properties defined on the symbols? If not you could add them in the symbol definition as a placeholder, then update the symbols in the design. Then run a live verification and add the required properties from DxDataBook for the symbols with missing properties. This should (hopefully) add the missing properties in a lesser number of steps.
If you think training is expensive, you should try ignorance!
Rob, thanks for your suggestion but...
It turns out that although the properties are defined on the component they are as non-common properties. They were added to schematic before updating Property Definitions - my bad. But who knew right
I have been pointed in the direction of a script (by our support co.) which will delete and re-add properties to effect the change from non-common to common. See attached. It has just sorted out 863 components for me - phew, much relieved.