Unfortunately there is no other way to include the wire/multicore part number in the cavity chart. We do have roadmap plans to extend this, however I would recommend that you look on the IDEAs website to ensure this doesn't get lost.
Note: for Capital users a custom table can be created which includes the P/N and any additional properties.
You didn't make any comments on the Maximum Width of 15 for Decoration Set, so does it mean that currently it is still impossible to modify this value?
As for 13.1 SP1406 (latest version) this has not changed - still a limit of 15 wide.
I see you found and Promoted D8275 for this.