Currently, I only have a TV with HDMI and SCART inputs. So I'm unable to test VGA right now. Doesn't the ioreg show the connector types even with no monitor connected?
The "connector-type" is not the primary concern... more about port assignments.
But, given your current scenario then, there almost nothing to do.
Your ioreg shows three connectors active for the ig-platform-id you're using (0x16260006).
Look at the connector data in the framebuffer for 0x16260006:
00 00 08 00 02 00 00 00 30 02 00 00 -> @0 LVDS
01 05 0B 00 00 04 00 00 07 05 00 00 -> @1 DP (0105)
02 04 0B 00 00 04 00 00 07 05 00 00 -> @2 DP (0204)
FF 00 00 00 01 00 00 00 40 00 00 00 -> @3 undefined, not used
According to your ioreg, your monitor is connected to the 0105 (@1).
I assume if you connected VGA, it would be connected to 0204 (@2), because it is the only other external connector.
You might try patching for HDMI (assuming your external port is really HDMI):
Find: 01 05 0B 00 00 04 00 00 07 05 00 00
Replace: 01 05 0B 00 00 08 00 00 07 05 00 00
And you could also patch the 0204 for VGA. I think VGA connector-type is 01 00 00 00, so:
Find: 02 04 0B 00 00 04 00 00 07 05 00 00
Replace: 02 04 0B 00 01 00 00 00 07 05 00 00
You might need to experiment with the flags at the end for the VGA case (those flags are not well understood):
Find: 02 04 0B 00 00 04 00 00 07 05 00 00
Replace: 02 04 0B 00 01 00 00 00 40 00 00 00
You could also try eliminating the 0204 (that would disable VGA):
Find: 02 04 0B 00 00 04 00 00 07 05 00 00
Replace: FF 00 00 00 01 00 00 00 40 00 00 00
And you would probably need to change the connector count:
Find: 06 00 26 16 01 03 03 03
Replace: 06 00 26 16 01 03 02 02
or
Find: 06 00 26 16 01 03 03 03
Replace: 06 00 26 16 01 03 02 03
or
Find: 06 00 26 16 01 03 03 03
Replace: 06 00 26 16 01 03 03 02