cracking the driver case

Yeah, I wouldn’t keep hammering that yellow piece with a screwdriver. On the XDT08, the housing is held together by eight 3×16 screws, and the parts diagram shows the housing as a two-piece housing set. The switch itself is part 650689-0.

That yellow piece you’re seeing at the bottom is probably the battery terminal/support area catching on the housing. When you separate the halves, work around the housing seam with a thin plastic pry tool and gently work the halves apart rather than prying directly against the yellow plastic. The same basic Makita housing procedure on these impact drivers is to separate the two shell halves carefully while keeping the yellow battery-terminal piece seated in the lower housing. Once you get a small gap, go around the perimeter and release the shell little by little. Don't force one spot. There may also be wiring and the controller sitting in the housing, so I'd rather spend five minutes working the seam than crack a $30-ish housing or pull a wire loose.