Ok i don't want to jack this up but i have a Burton TNT file guide.
If my side bevel is 1 degree and my base edge is -1 degree. Should I set the TNT file guide to 91 degrees since it should ly flat along the base as i drag it down the edge? Will this maintain that 90 degree edge?
Theoretically yes, but I have never seen a snowboard set up this way. There is not a negative base bevel, All factory bevels are no less than zero, not a negative 1. Maybe I am not understanding your meaning here, but you really have no need to put an obtuse angle on your edges.