You can start mission packs with AppleScript.
Quit TenebraeQuake.
Copy the folder of the mission pack to your "Quake" folder. The "Quake" folder is the folder that holds the "id1" folder.
Open the application "Terminal" which is part of the MacOS X installation.
Change to the directory that holds the TenebraeQuake application. For example: "cd /Applications/Games/".
Start the TenebraeQuake application by appending the command line parameter "-hipnotic" or "-rogue". For example: "./TenebraeQuake.app/Contents/MacOS/TenebraeQuake -hipnotic".
Quit TenebraeQuake.
Copy the folder of the mission pack to your "Quake" folder. The "Quake" folder is the folder that holds the "id1" folder.
Open the application "Terminal" which is part of the MacOS X installation.
Change to the directory that holds the TenebraeQuake application. For example: "cd /Applications/Games/".
Start the TenebraeQuake application by appending the command line parameter "-game" followed by the name of your mission pack.