To start Serpent Isle with cheat mode enabled, you have to edit \Ultima VII - Complete\SERPENT\dosboxSERPENT_single.conf

Open the file with wordpad and change the line
serpent.com
to
serpent MANIMAL

Save and start the game with the link created by the GOG installer ("Launch Ultima VII - Serpent Isle").

Sounds like PC instructions. How would that apply to a Mac user?

It's the solution for DOSBox, didn't know you're using the Mac version.

I can't check it step-by-step here, but basically to adjust the settings for a single game, look inside the gamebox (ctrl-click and choose “Show Package Contents”). Look for .conf files. Usually there is a DOSBox Preferences.conf file, which contains performance and compatibility settings with tips for what each setting does, but I'm not sure if it includes the shell commands to start the game:

Search for these entries:
[autoexec]
@echo off
mount C "..\SERPENT"
cls
c:
serpent.com

exit

and then change "serpent.com" to "serpent MANIMAL"

Thanks, I managed to do just that, and saved the edited .conf file. But as far as I can tell the cheat mode hasn't activated within the game, or I'm just not figuring out how to make it come up. If anyone has any experience with running it in this particular game I'd love to know how it's done.

When you press the F2-key, a cheat option menu should overlay the game. (On some laptops the F-keys are only accessible by pressing another function key, otherwise the keys do stuff like turning up and down volume etc.)

Yeah... the function buttons aren't doing anything for me. And I've gone into System Preferences and tried checking the "Use F1, F2 etc as standard function keys" box and still no dice.

While in cheat mode Alt+1 gives you the option to enter an number from 0-134 to play a sound.
(Alternatively Alt+6 and entering numbers from 0-69 plays music)
Check if that works.

No, that appears not to work either.

Is there some other location I need to launch from other than the icon in my Applications folder?

Hmm, looks like cheat mode isn't activated then. But there is a way, because the game is the same on Windows and Mac, only the DOS emulator is slightly different (DOSBox and Boxer). The cheat mode definitely works on Windows, I checked it.

Although it's for the original release and not for Silver Seeds (like the GOG version), you can try altering serpent.com to serpent PASS to activate cheat mode, but it doesn't work here on my installation.

Which file inside the package did you edit?

Just tried that too, still nothing.

I edited both the dosboxSERPENT_settings.conf file and the dosboxSERPENT_single.conf file as they both had text matching what you said to look for. No adverse effects from that, but no cheat mode either.

The icon in the Windows version starts DOSBox and tells it which conf files to use
"\DOSBOX\DOSBox.exe" -conf "..\SERPENT\dosboxSERPENT.conf" -conf "..\SERPENT\dosboxSERPENT_single.conf" -noconsole -c exit

Withing dosboxSERPENT_single.conf are the start commands for the game.

Check the properties of your icon, maybe there's useful information there.
Damn, I'm not OS X savvy enough to give a quick answer. It's pretty clear what to do, but not how to accomplish it on a Mac :-/

When you open the gamebox, and look inside the package, is there a "Launch Ultima VII - Serpent Isle" link? If so, try running it (while dosboxSERPENT_single.conf is still altered to serpent MANIMAL).

Also try altering it to "serpent manimal", maybe there's a weird case-sensitivity issue.

Sorry, no such link. U7 parts 1 and 2 are wrapped up together in the link called "Ultima 7: The complete edition".

Pretty deep inside the package there's a SI.exe file but I'm not sure how to open that on a mac, or if it would help.

When you ctrl-click on the gamebox and choose “Show Package Contents”, you can double-click on the desired program. But you need to run serpent.com with the parameter manimal.

It's not set up that way on a Mac. When I click on "Show Package Contents", I get another folder called "contents" inside of which are the following: folder "_CodeSignature", folder "Frameworks", Info.plist, Licence.txt, folder "MacOS", PkgInfo, and folder "Resources." Resources contains a .boxer file called "Ultima VII The Complete Edition.boxer" where the .conf files are for each game, and the .exe files.

There's no simple launch option for each game individually, you have to launch both from the original launch link in the Applications folder.