Ok I have finally found a solution to my problem with thanks going to Werner for tremendous amounts of help

After some playing around I found that the command 'loadkeys us' would successfully change my keyboard layout from de to us. But since I am remastering this image for another user, I needed to plan for as little input on their part as possible (the system should be working as they need it when it starts up). To avoid having them type the loadkeys command each time the system boots, I created an extremely basic script to just run the command:

Code:
#!/bin/bash

echo changing keyboard layout
loadkeys us
Obviously the echo line was for testing purposes and can be omitted. I placed this script in a folder where a few other unrelated scripts are running at boot (/etc/rcS.d) and was pleased to see that it actually worked as intended.

I'm still not sure why the keyboard was changing to German in the first place since I was using the En version of Knoppix, but this workaround will suit my needs. Hopefully this solution will help some other people as I had been searching for some time and could not find any working solution.

Once again many thanks to Werner as I could not have reached this solution without his assistance.