I've never had much luck trying to change the origin for a set of ordinate dimensions.
My theoretical method for next time I try would be:
(1) Figure out which of the dimensions was created first, i.e. is the one that was toggled to ordinate to start the set.
(2) Try to redefine attachment on that dimension. I don't know if it will let me do this. It might just let me change the non-origin half of the dimension.
(3) If that doesn't work, maybe toggle that dimension back to a "normal" dimension, then redefine its attachment.
(4) Once I've redefined it, toggle it back to ordinate.
I've tried a variety of things in the past, but always given up and deleted all the dimensions and recreated them with the new origin. So much for efficiency.
