Terminal Software:

Installed:

Mac OS 7.5
Kaleidoscope 2.3.1
Kaleidoscope Scheme "Black Attack Green" - modified

Apps Used:

Adobe Photodeluxe (It's like Photoshop lite)
Apple Script
Resedit
Durandal Terminal Browser
Hex!
SoundEffects 0.9.2

I used Resedit to modify the DLT #128 resource of the Durandal Terminal Browser. From a screencapture using Marathon AO, the deep red colored Terminal Bars were put into PICT format. I pasted these into the PICT resource of the Durandal Terminal Browser, and added them into the DLT resource.
I was careful not to modify the size of the User Item box, but adding PICTs was fine. I renamed DTB to 'Marathon Terminal Browser' (Due to its interface adjustment)

I compiled various Terminal texts and Images from the Marathon Trilogy/3rd party scenarios. Using HEX!, and some merged dummy-levels I created the Map (.sce2) file for Terminal Browser to read.

I edited the Kaleidoscope scheme "Black attack Green" to have all black Icons, as well as a Black square instead of the Apple for its Menu Icon. Since everything's black, it doesn't show.
Along with a black desktop pattern, and Setting the background window color to Black, it almost completes the total Black look.

Used Resedit, I copied the 'Startup' from Marathon1, and the Terminal Logon beep sounds. Using The Scrapbook, I pasted them there, then dragged them to the desktop to create actual .snd files out of them.
SoundEffects 0.9.2 was used to edit together, then export as one sound the Startup/Terminal logon sounds.

I used Apple Script's "Record" feature to write an applescipt. It launches the Startup/Terminal logon sound, then opens Marathon Terminal Browser.
This all occurs on startup, since I placed the script in the Startup items folder. Another sound, an eerie clip from the song 'Solaris' I placed in the Shutdown Items folder. It launches when the system is shutdown via Special Menu (if a external mouse is connected).

All alteration I had done thus far was to non-system software. Again using Resedit, I edited the Courier Font (which I set as System default with Kaleidoscope). I altered all font sets (Bold, Italic, Reg.) "+" symbol to have a custom drawn Marathon Symbol. Just for effect. :-)

Resedit was used to open the 'System' file, and the KCHR resource. This allowed me to remap the Arrow Keys, Pageup/Pagedown and Enter keys to custom locations on the keypad. ** During all these alterations, I had a non-altered ADB keyboard/mouse plugged into the ADB port of the edited keyboard.
The DSAT resource was altered to modify the Startup/Shutdown messages to something less - Macintosh like.

A Startup screen PICT is placed in a New Resedit file with the ID #0, instead of the default #128. This file, named 'startup screen' is placed in the System folder.