Plugging in towbar electrics doesn't affect the AWD as far as I know. Nor should it.
The car detects the front wheels are slipping so transfers power to the rear wheels through a diferential of some form or another. I think the max power transfer is a 70/30 split.
Also from a personal view, the freelander isn't exactly "capable" offroad. Just my own experience while offroading in the Discovery ... we had to save more of them from the mud than anything else
