Reading the config.txt docs, I found this:
These values are valid if hdmi_group=1 (CEA)
hdmi_mode=1 VGA
Does this make the output on my HDMI port be VGA? I have a cable that with a VGA and an HDMI ports, but no converter. Would I be able to use a VGA monitor with that cable and the Pi outputting VGA? Or is this something completely different?
As noted in the documentation you linked:
hdmi_modedefines screen resolution in CEA or DMT format
In this case, VGA would seem to be referring to the resolution, rather than the VGA connector. As noted by Wikipedia:
Through widespread adoption, the term has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector, or the 640×480 resolution characteristic of the VGA hardware.
Converting HDMI to VGA is actually rather more complex than just flipping a setting, as HDMI is a digital protocol and VGA is analogue. You typically need an active converter, like this, to make it all work properly.
