There's basically two methods for developing a feminine voice. The first, which many find far less effective is essentially to use the 'mini mouse' voice and learn how to make a natural sound by working your pitch downward and toying with inflection and tone. The other, which most professionals and successful transwomen will tell you is far more effective, is very similar to vocal training. My voice coach in Chicago has described finding a feminine voice to essentially be learning how to sing in a very subtle manner by learning how to find tune your pitch, tone, inflections, etc. After just over a month and 3 lessons, I feel like my voice has made a ton of progress. I definitely don't think I sound feminine yet, though I have had a few moments where I feel like I sort of got it ever so briefly, but I can already feel more control over my voice and my range whether I'm holding normal conversation, practicing my lessons, or singing in the car. So the short answer is yes, but I imagine learning how to actually sing sounding naturally feminine would be a whole other step up in difficulty. But, when there's a will, there's a way!