The answer again is using Properties.
This workflow is not recommended though it has the benefit of tying the Keynote to the Description in a way that it is more difficult to edit.
01: Write your Classification
02: In Property Manager create a new Property and make it available for the Classification already created
03: Here's were the process starts to break down (and why you should use Properties). You will need to create as many objects as you have items in your Classification and assign one classification to each. OTOH you can do this at the end of the project and have the list only show what is available.
04: Create a Schedule that has the Criteria "All 3D Objects" and Classification = "Yours" with "Has Value". There might be other options that work here.
05: In Schedule Fields add the one for Classification Description and the one created for the Property. You can add Id or others if you want but they are not necessary.
06: Open the Schedule and go File->Interoperability->Classifications and Properties->Export (Excel Worksheet)
07: Open Excel File and selected the items inn the column that matches the Property and make them equal to the ones on the column for Description. Save the file
08: In AC go File->Interoperability->Classifications and Properties->Import and select the Worksheet
Now the created Property matches the Classification Description and the Label can read it.
If anything changes just redo steps 06 to 08 and it will update without issues.
If you think this is too difficult or cumbersome or GS should make it easier let me remind you that if you use regular Properties you don't have to do this but you will need to do other stuff.