As for altering quests, you'll have to contact Kratzean when he is on, as I am relatively certain he is the only one that is still fairly active and that has done anything like that. I basically assume that if there is something that seems like it can be done but I don't know how, that Kratzean does, and I am relatively certain he did something similar in his Atlantis Mod, though being without CI I cannot open it and see. :rolleyes
I'm not sure about making skirmish gods have voices, but you can alter the voices and sound in the game by alternately changing/adding to the sound files of the game (for which you need something that can open, edit and save the files, I don't remember the format but Audacity and Amarok work for nearly anything--I'm not sure if Audacity works for Mac, but I'm pretty sure Amarok does) and changing the calls to that file in the scripts, the latter of which I don't know how to do, but suspect that Kratzean could help with, too.
Know, though, that the most that most people do is make their own .lnd files and skirmish maps; Changes to the main quest maps always detracts from the story for me, including, except perhaps on Land 4 which is terrible for your alignment if you are good, Cache's cheats. There was something a while back called BW Eruption, which hasn't worked for me (and from the reviews of it I deemed that it wasn't worth the bother) that added a quest to the game (from what I can tell), and there are numerous mods from Kratzean such as the colourchanger and the Atlantis Mod (in which I know from his YouTube video Kratzean included new miracles), and the only special tools I know of for changing the deeper mechanics and not just basic things in the script are the CHL programs.
All of the things in your last post sound possible. To turn Land 1 into a skirmish, I believe all you would need to do is copy the script "Land1" to the Playgrounds folder, and make sure that your citadel is already built and not in the process or your game will end as soon as it begins. Kilroy's Training Ground map includes similar features to what you describe (I presume that the wall of stones blocking the enemy creature was Kilroy-inspired?), which may help you out.
I do not know of any reason that you can't make new .lnd files in Mac, but then, I threw down my last Mac in disgust two years ago and have never managed to get too into them. If you could explain to me, Grem, why this is so, perhaps I can look into a way of circumventing it? ???