Is there any known case of a pin pad device being compliant PCI v2 but by changing just a software component it becomes PCI v3 compliant?
I'm going to assume that when you say PCI v2 and PCI v3 you mean the PCI PTS POI standard - ie the one for physical devices that include pin entry or are secure card readers. I’d personally be very surprised if a software upgrade changed the appropriate version number, because the hardware security profile changed between v2 and v3. The easiest way to check is on the PCI SSC website. All PTS devices are listed here: https://www.pcisecuritystandards.org/assessors_and_solutions/pin_transaction_devices