Although the Pedal assist ratio can be set using the program software, I'm pretty sure that you will still need the BAC-601 Smart Display unit to be able to select the required pedal assistance level which needs to be done each time you switch on the battery, because the PAS is automatically re-set to "level 0" (Off) when the battery is turned off.
I briefly tried disconnecting the BAC-601 Smart Display earlier today on my latest MP4 controller and the pedelec does still work without it, although with my existing power settings I find it is a bit too aggressive.
If I didn't have the BAC-601 Smart Display it should be possible to reduce the Pedal assist ratio in the software to tame it down a bit, but as I much prefer having selectable level settings I have plugged the Smart Display back in, which means I don't need to mess about with the existing parameter settings.
If you have the latest version of the vector controller you don't need the Smart Display unit for the pedelec to work, but after using it many times over the past few weeks, I would not enjoy having to use pedelec without it.
Alan