Thanks you for your valuable suggestion Jeff.

You can add additional values to the selection fields by editing the translations.

Go to Administration > Customization > Opportunity

Look at the fields, oppo_stage and oppo_status. You can edit the selection lists.

NB - Be careful not to remove or change the In Progress caption code as much existing functionality expects that value to exist.

But adding the values into the selection list does not mean that these 'mean' anything. You will need to think about your workflow too.