Ok. When you detune a half step, technically, the position where an A chord or a G chord was is now an A flat chord and a G flat chord. But that gets really confusiong on the guitar. So it is universally accepted that when you're detuned and you tell someone you're playing a D chord when it's really a D flat chord, you just tell 'em that it's a D chord but make sure they know you're detuned. It would be nuts to relearn all the positions for everything all over again.

However, if you're in drop D or DADGAD or something other than an equivalent to standard tuning, you're screwed.