Can the stock fog light wiring handle HID lights? If so, not a lot of room between the mounting area to the fender? Has anyone done this,? If so what's the best (biggest) HID stuffed in that area? Brand, size, model Etc?
Check the OEM light's Watt and Amp ratings and make sure the replacement is close to the same. If the Watts/Amps go up by much on the replacement, you'll pop fuses. In that case, you'd need to rewire completely, or use the existing switch to run a relay that controls the newer lights which would be wired separately.