I have a Nikon D3100 and a Yongnuo YN467 speedlight. What I need is to use thee AF light from the camera body, since I realize it is really better than the speedlight one. Is there any way to achieve this? Every time you put the speedlight on the hot shoe, it activates the speedlight AF light.
It may or may not help, but: if I turn the AF assist light off on an SB900, my D300 will use the built-in AF assist light, even with the SB900 attached. If your flash has the option to turn off it's AF assist light, that might do it for you.
If you want to use your in-camera AF light, you must disable hotshoe flash monitor pin, but this causes TTL to stop working and flash will trigger at minimun power, just usable in flash M mode.