Q:

Changing slopes derived from DEM using ArcGIS Desktop? 

I have a DEM for a region over which I want to simulate an ecological process.   I would like to run several simulations for the same region but I want to alter the topography for the simulations.   Most important, I would like to alter the slope (and probably aspect) in various ways.   I am working in ArcGIS Desktop and I extracted the slope from the DEM but I have not found any way to manipulate the slope or even access the slope values with their coordinates.   Running the process requires several other layers so I would like to remain within the parameters (coordinates, datum, ellipsoid, etc.)  of the original DEM.   
Is there a way I can alter the slope output, which is currently a raster?  
Could I, for example, make the whole region 30% slope with a south aspect?   
Is there some other way to generate custom slope files that will be consistent with the other layers? 
I am using an ArcGRID DEM from the NED.  
Perhaps a different starting point is more appropriate, such as a contour map?    

A:

A contour map is rarely a good starting point, especially if you already have a (gridded) elevation model.  Contours are cartographic, rather than topographic, features. 
Having said that, if the DEM was derived from a contour map to begin with, then maybe you should return to the source.