OK, here's the basic texture with the eyes swapped out, as per the above pic:
Looking at the Bandon mod, it's set up as follows:
Base texture - n_darthband01_h.tga
DS1 texture - PMHC08D1.tga
DS2 texture - PMHC08D2.tga
My texture is named N_DarthBand01_H.tga, the same as the original. If you only want to use it for the Dark Side transitions, just make a second copy and name them PMHC08D1.tga and PMHC08D2.tga, then throw them in your Override folder (overwriting the existing files). If you also want to replace the LS/neutral skin, throw in a third copy that you leave named N_DarthBand01_H.tga.