It’s impossible to prove a negative, but I’m going to say that I have never seen such an option, and it seems unlikely given Wizards’ design for them to make a generic option along these lines. A feat specific to a certain race or creature, sure: then you can know exactly what it is you’re offering. But if the feat or whatever is generic, then the authors of the feat have no idea just how much DR they’re improving, and they may possibly be unaware how much they are improving it.
For example, if the feat were so broad as to apply to any amount of any type of DR, and add an additional restriction of “-and-slashing” to it, a lich’s DR goes from 15/bludgeoning-and-magic to 15/bludgeoning-and-magic-and-slashing, sharply limiting the number of weapons that can actually bypass it (executioner’s mace from Dungeon vol. 135 is the only wieldable weapon in the entire game that could do it; bite attacks could also). The lich’s DR was always good; this makes it basically perfect.
Potentially worse, though, is someone who had just DR/magic, since usually DR/magic is close to meaningless. Making that DR/magic-and-slashing makes it much more significant. Since DR/magic is close to meaningless, designers are often comfortable putting far larger numbers before than slash than for other forms of DR. Such a feat turns that overly-large number into something very meaningful, and that’s a big deal.
Finally, Wizards was always (overly, really) conservative with DR for players. Since there were relatively few feats written just for the DM, and feats were often seen as a “player thing,” it would be out of character for them to write a particularly flexible DR-changing feat.
Considering all of this, and my rather-extensive knowledge of the options available in 3.5, I’m going to say this doesn’t exist in the general case. There may be options for, say, a shifter or warforged or something specific like that, but not just a general use one. Additionally, lycanthropes never saw very much support, so I tend to doubt there is one just for them. For the sake of double-checking, though, I have looked through the Savage Species feats, as Savage Species is by far the most likely book to find this kind of thing; it does not.