[roxxor]

For anyone following this thread, I have some information. On the X3 forums, it was discovered that even modifying the US switch wouldn't work, it actually requires the Euro switch. After that, the same coding changes I made to my G01 X3 (which was just changing the lighting related codes to match the Euro Version) worked to get the rear fog lights working, and ideally, changing those same line items should also enable them on the G30. After you install the switch, the line items changed should be:

Confirmed working as of 3/15/2020. However, you must verify you have the LED modules first. Please read rest of thread.
All changes are in the BDC_Body2 Module, in the 5FA9 Cafd file
NSL_Verbaut: Change this to "Verbaut"
LCE_BEL_LIN_VAR: Change to match your existing switch, plus "NSL". For example, mine was "39_BEL_PL_FLC_NSW_NIVI", so I changed it to "40_BEL_PL_FLC_NSW_NSL_NIVI". This keeps the incorrect light switch variant error from showing up in ISTA.
LIC_LOG_LAMP_2_OUTPUT_CHANNEL_DATA: Change this to "G30_ECE_Code"
LIC_LOG_LAMP_2_OUTPUT_CHANNEL_INDEX: Change this to "G30_ECE_Code"
LIC_NIVEAU_OVERRIDE_DATA_0: Change this to "UNK_PARAM_1"
LIC_NIVEAU_OVERRIDE_INDEX: Change this to "UNK_PARAM_3"
LIC_VERSION_DATA: Change this to "UNK_PARAM_5"

HOWEVER, when I tried the codes, they did not work. Similar to sgimips. I decided to look at my tail light to check the wiring, and lo and behold, my 2020 G30 is missing the wires that Newtis says should be there for the rear fog lights. I won't be able to test adding the wire until mid-next week, but for those who bought the Euro switch and can't get it to work with just the coding, I would double check your wiring.