How to alter "Column Type: CUSTOM PROPERTY" dropdown

1. Create an assembly

2. Insert, Table, Bill of Materials...

3. Table Template: bom-standard

4. Right-click "A" or "B" or "C" etc.

5. Insert Column (Left or Right)

At this point the little window with "Column Type:" and "Property Name:" appears.  How do I alter the values in this dropdown.  I've already changed the "properties.txt" within *\SolidWorks 2010\lang\english and that now appears in file properties, but there seems to be no way to change the BOM properties.

TIA  -  Abraham

SolidworksBill Of Materials