On page 30 of the Nucleus User Guide the following text (in red) may be interpreted such that mulitple Key Assigns (USB) can be assigned to 1 Nucleus Soft Key as is the case with DAW CMDS.
"Note that modifiers can only be assigned within the same command type as its modified function: DAW CMDS or Key Assign."
For clarity, please note that this is not possible or actually needed. If a 2nd Key Assign is programmed to a Soft Key that already has one, the current programming will be overwritten. Please refer to page 28 of the Nucleus User Guide for more information.
The Nucleus User Guide can be found here.