HEC-RAS can incorporate non-Newtonian effects in any unsteady flow simulation including 1D or 2D. But the current version of HEC-RAS does not include non-Newtonian effects in steady or quasi-unsteady flow.

Therefore, the non-Newtonian editor is an Option in the Unsteady flow editor.
 Select the Non-Newtonian Editor from the Unsteady Flow Options Menu.  HEC-RAS Non-Newtonian editor.