Hopefully this is the right board for my question, which is:
If I disable all USB ports, but then use a PS/2 to USB converter, will
that USB device work? Thank you.
Yes, if you had a PS/2 to USB converter that works when the
USB ports are enabled, it would continue to do so
afterwards. The enabling or disabling of the USB ports does
not mean "USB in general, any and all USB", it only
determines whether the specific ports being addressed, on
the board through bios or in OS, will be enabled. Similarly
if you disabled them and installed a PCI USB controller
card, the card's ports would work still unless you also
disable those additional ports.