You can try these methods:

• Edit the MAT file to change the RGB value of the hair (if applicable; assumes the MAT file has some base color other than white, through which the existing texture is multiplying)
• Edit the MAT file to change the textureMap path to a platinum blonde texture file, then resave under a different MAT file name
• Rename your platinum blonde texture file to be the same as the existing file (first resave the existing file under a new name)
• Convert the existing texture file to platinum blonde by desaturating or lightening somehow (probably not a good idea)