Meanwhile, I answered my own qustion... this tool is AMAZING! That much credit up front!
In order to resolve the problem with special characters, I simply put double quotes around the key and it worked.
So, the result would be:
C:\>RegSecEdit.exe -u:useruser -p:"SYSTEM\CurrentControlSet\Enum\HID\VID_413C&PID_5116&MI_02" -b:Machine -i:0 -a:0 -r:983103
In order to resolve the access denied issue that followed, I simply used the common workaround on Windows Vista to run the command under the SYSTEM user. Admin folks will know what I am talking about.
Cheers on this great tool! - Thank You!