Hi, Masaq, everyone:

A few suggestions: When you open the file, select to open it with NO mipmaps.. you don't need them. When you are finished editing, save to dds and in the dds dialogue window, choose the "generate mipmaps" and save with the same number and type as the original dds file you edited. (no need to go though all the canvas sizing, copying and scaling, etc).

If you're handy with a mouse as a brush, just create a layer and paint right over the parts you want to change choosing multiply, hardlight, or over layer properties to get the effect you want, along with the layer transparency and color adjustments to the layer you can get some really good results. You also don't have to stay right inside of the edges unless they overlap onto another plane part, so exact selections are really unnecessary in most cases.

Have fun