A violin "air freshener" wouldn't be that hard to make.  Though I'd say it would be more marketable to call it a "custom scenter for string instruments" or something.

Find a pen cap or small marker cap that will fit snugly in the round "dot" of an F without needing to be jammed in or so loose it might fall into the body of the instrument.  Drill out the closed end of the cap, so it is more of a tapered tube.  Then take 3 little pieces of cotton.  Roll one into a little ball and stuff it into the cap.  Then make another little cotton ball and put a drop of an essential oil or scent oil or cologne you like on it.  Put it into the cap.  Then put in another little ball of cotton.

That way there isn't much (if any) risk of and of the essential/scented oil or cologne dripping and getting on the wood.  Not a lot of risk anyway, since it would only take a drop on the cotton.

Bet it would change the scent of a violin (and case, if it is kept in the case) within a week or so at most. 

I scent some of my instruments by just keeping a scented item or a cottonball with a drop of some scent in a little bag in the case.  But the violin isn't as open to the air as a guitar or oud is.  So it would take longer, and something that could put a little scent both inside and outside would likely work better/faster on a violin/fiddle.

People can laugh, but the scent of an instrument is part of the experience of playing it, especially with something like a violin where it is so close to the player's face.  If one doesn't like the smell, it only makes sense to change it to something one likes better and that might even put the player into a playing sort of mood.  Done carefully, I don't think it would risk hurting the instrument.