Can an MK3-USB cable be used (instead of MK2-USB) to upgrade the older firmware (e.g. on the MultiPlus) which requires the use of VE.FLash? I assume it would have to be done from the Windows machine, since that's the only OS that VE.Flash works on - correct?
It rather depends on the unit you have and the chip and how old the firmware is.
https://community.victronenergy.com/questions/178043/interface-mk2-or-mk3-usb.html
And the manual....
https://www.victronenergy.com/live/updating_firmware:updating_ve.bus_products
On my Multiplus was a sticker on the chip that is in a socket so it can be replaced. It had the 7 digits and then “.VFD” after it. On my case it was supplied with Version 413 it seems. I got it with V498. Updated to 510, but still bricked. 
