Based on "testing" during the drive into work this morning, yes, I can override the shift points programmed for D in Drag Mode by shifting manually. However, with an 8-speed trans, it runs through the low gears pretty quickly.

EDIT: I also spent some time last night watching video of last week's MSHS race in Florida (see https://www.youtube.com/watch?v=Lb7Av7BCAAQ; and thanks to member "Dart 500" for the link). Not only are the RTs all over the place, so are the strategies I see people using to slow their cars down to make an index.