AudioMIDI's no brainer deal.

[DarkStar]

Banks only have 64 presets - so you'll need to make a new bank. Just save it over the default [Orbit], rename it, and then select "Save Bank" and create a new bank.
'Tick

Got it, thank you. But that'll overwrite the original Orbit, won't it.

How about:
-- Save Bank, to create a new bank
-- then work with those copied presets to my heart's content?

I'd rather not experiment too much until I understand how much damage I can do.

[Big Tick]

It would be the same results. The original bank (with its original Orbit) will still be there, unless you overwrite the bank by mistake.

[DarkStar]

OK,

So "Write" writes the modified preset data into the bank loaded in memory, and "Save" writes the Bank or Preset to the "presets" folder on disk, after I have chosen or typed in a finame.

Next:
(a) how do I add a preset to a Category in the Library?
(b) how do I remove a preset from a Category in the Library?
(c) How do I add a keyword to a preset or remove a keyword?
(d) I set up a Sequence and enabled [MIDI out] but could not get any MIDI out- what have I missed? Or is that just for MIDI CC automation messages?

[Big Tick]

(a) how do I add a preset to a Category in the Library?

Drag the preset from the bank, into the library.

how do I remove a preset from a Category in the Library?

Drag it around in the library.

(c) How do I add a keyword to a preset or remove a keyword?

Keyword search uses the preset name, and the fields in the preset information.

(d) I set up a Sequence and enabled [MIDI out] but could not get any MIDI out- what have I missed? Or is that just for MIDI CC automation messages?

Yes it's for Midi CC. When Midi Out is enabled, moving a control will send a Midi CC out (provided you have assigned one for this control using Midi learn).

[DarkStar]