Details are in the docs at http://exult.info/docs.php#path_config_osx
Exult no longer uses ~/.exult.
My advice is to backup and delete your ~/Library/Preferences/exult.cfg
It will automatically pick up Ultima 7 games installed to /Library/Application Support/Exult (note that this is NOT ~/Library/Application Support/Exult).
Meaning, that it will pick up
- BG in /Library/Application Support/Exult/blackgate
- SI in /Library/Application Support/Exult/serpentisle
If you put the games in there you don't need to edit ~/Library/Preferences/exult.cfg
Mods and patches will also be automatically used if put into the corresponding games folder, e.g. the Keyring mod would need to be put into /Library/Application Support/Exult/blackgate/mods.
Patches you have made or want to use also need to go to its game folder, e.g. /Library/Application Support/Exult/blackgate/patch
The data folder defaults to /Library/Application Support/Exult/data. If you put the digital music folder and the sfx files in there Exult will automatically use them for the correct game. If you have both the SoundBlaster and Roland MT32 pack in there, Exult will default to the Roland MT32 pack. If you want to use the SB pack you will need to edit exult.cfg (see http://exult.info/docs.php#wave_sfx).
Savegames are saved to ~/Library/Application Support/Exult/gamename, e.g. a Blackgate savegame will be found at ~/Library/Application Support/Exult/blackgate/exult00bg.sav, a Keyring mod game will save to ~/Library/Application Support/Exult/blackgate/mods/keyring/exult00bg.sav.
Also if you use the app bundle, Exult will default to use the data folder inside the app bundle, before looking at /Library/Application Support/Exult/data for additional data. This means that if you really want to you can store the digital music folder and the sfx files in exult.app/contents/resources/data. But be cautious, f you replace the app bundle with a newer version you might lose your music and sfx files if you do that.
This might be confusing at first but if you delete your old exult.cfg and use the new default paths you will find that it's now much easier on OS X.
Please feel free to ask for additional help here

Edit: updated with changed paths