Customise default Flag categories

[Debrastus]

Is there a way to fully customise the Flag to-do items without having to customise the flag for each email. I would like to add new custom to-do items in the Follow Up section under Tags so that my custom list is always available to add a custom flag to any email without selecting each email individually and then having to type in the custom name for the flag.

I tried just going to Follow-up and then choosing Custom and typing a new category and then OK, but it's not there when I go back in.

Hope this makes sense.

Thanks
Debbie