[GRASS-user] Change value of cells in raster map

[Rich Shepard]

   I have two raster maps both of which have the value of all cells as 2,
with the label 'Category 2.' I want to change the value of all cells in each
map, one map to 0.0 the other map to 12.5. r.category allows me to change
categories but not values and r.mapcalc allows me to create new maps with
cells having a value based on the expression.

   What I fail to see is the appropriate module to modify an existing map by
changing the value in each cell. Please point me in the right direction.

Rich