Qatar, I assure you that permanent retraction is entirely possible. My skin stays back continuously of it's own accord with no additional measures, and has always done so; similarly, it will stay forward. I am sure there are other people like this, but realise this isn't the case for everyone.
I'm also interested in the possibility that the foreskin may apparently reduce in length. I doubt that it can shrink in the sense that there is less of it, but wonder whether it might lose some elasticity and contract in length. This may manifest as a plumping out of the shaft skin, or be taken up in the development of deep shaft wrinkles (as described by others). If this is so, then I also wonder if any such contraction is reversible by skinning forward and stretching.
Of course, everyone is an individual with different sizes, shapes and retraction abilities, so any such effect is unlikely to be universal. As Kylar says, for him there is no effect. As an experiment I have taken a photo of my skin forward to compare at some time in the future after extended retraction.
My belief based on my own circumstances is that retraction has REDUCED odour to minimal, and smegma is now non-existent (even without daily washing). This seems to be the experience of most, but again everyone has their own experience (as Fabik has described).