Well, I have not been able to edit preferences, and would still like help with this. However, I -have- managed to figure out personality. For anyone interested, I borrowed data from the brainwash script from Vjek at :
http://dl.dropboxusercontent.com/u/1339319/df_scripts/34.10/brainwash.luaBasically, I went into the Lua in DFHack, typed in 'unit=dfhack.gui.getSelectedUnit()' with my k cursor on a unit, and then typed in 'unit.status.current_soul.traits.ANXIETY=1'. Vjek's script, unfortunately, is not very versatile. It seems to be a manner of 'either you want your dwarf to be as he/she is, or the best dwarf ever!' If anyone ever enjoys writing scripts, you may wish to create a DFHack script that allows for more controlled augmentation ('select dwarf, type in stat, type in value') with some help and menu items.
Anyway, I'll keep trying with preferences...