Hello Jamie,
You can load the temperaments that are included with Hauptwerk using 'Pitch | Load temperament ...', or via the 'Pitch' large control panel ('View | Large floating control panels ...'), for example.
These are the mean-tone temperaments included:
- Mean-Tone: 1/5 Pythagorean Comma
- Mean-Tone: 1/6 Comma Modified
- Mean-Tone: 1/4 Syntonic Comma, Pietro Aaron
- Mean-Tone: 1/6 Pythagorean Comma
I can't actually remember the exact intervals that they use, I'm afraid (I based them on some tables many years ago, when Hauptwerk v2 was originally being developed), but I'd suggest trying the 1/4-comma one to see.
You can create a temperament file yourself manually by basing it on one of the existing ones in:
[Hauptwerk installation folder]/HauptwerkSampleSetsAndComponents/Temperaments
Make a copy of an existing one, rename the copy appropriately, then edit it in a text/XML editor to give it a new UniqueTemperamentID in the 'user' range 800000-899999 and appropriate Name and ShortName, then set PitchHz for each MIDINoteNumberOnEightFootStop in the range 0-132 (middle C on an 8' stop is note number 60).
A Hauptwerk user created an on-line Hauptwerk temperament file generator utility at one point, but I'm not sure whether that website still exists.