Once you have assigned patients to your Fee Categories, they shouldn't be re-ordered or the patient assignments will also change. For example, below is my original Fee Category listing, with 'Standard' placed in the first slot.
And below is a patient who is assigned to the 'Standard' fee category.
If I later decide to rename or swap Standard with Workcover, all the patients I assigned as Standard will now be displayed as Workcover instead.
This would also effect reporting based on fee categories. For example at the time of completing a transaction, it records the fee category of the patient at the time.