Unless my copy is totally different, Change Gamma is not what you should use to change the gamma of your intensity maps (bump, trans, displacement, etc.).  Image Gamma is.  As described it will "change the texture gamma values on either the current material, the current figure or all props and figures."   In other words, it will make the gamma on all your images the same for a given selection (material, figure, or scene).   Image Gamma will let you have different gammas for maps with different purposes.