Thanks for all the advice. For those that may want to know how to do this.
For standard Balloons, you pick the Table tab and select the table, pick Properties, then the BOM Balloons tab in the properties dialog.
In the BOM Balloon Parameter field, you enter asm.mbr.cparam.find_number
Where find_number is the component parameter assigned in the assembly.
[cid:image001.png@01D05022.9D3C9DD0]
This works for both the standard balloon types in Creo. (simple & split)
I then changed the balloon type to a custom quantity balloon.
The existing symbol looks like this:
[cid:image007.png@01D05023.E7604D70]
I did not edit the symbol.
The table properties now look like this:
[cid:image002.png@01D05022.9D3C9DD0]
The symbol works without editing.
[cid:image003.png@01D05022.9D3C9DD0]
David Haigh