I'm sure all pipe smokers eventually run into the problem of having some tobacco that has become too dry. There are numerous methods of rehydration, some more sophisticated than others. My last batch of Gray Ghost from C&D was a little too dry already when I got it, so I have been rehydrating small quantities of it as I go along.
My usual method of rehydration is to put some tobacco in a Mason jar, then place a small medicine cup (of the kind that you get any time you buy any kind of liquid medicine these days) upside down on top of the tobacco. I moisten a little tissue paper, fold it into a square and squeeze all the excess water out, then place it on top of the inverted medicine cup and close the lid. Give it 24 hours or so before smoking any of it. Sometimes it might also help to take the cup & paper out and mix the tobacco up, because the top layer will be more moist than the bottom, then return the cup & paper to their positions and give it more time. I use the cup so that the moist paper does not come into direct contact with the tobacco.
Another method would be to take a small amount of the dry tobacco and mix it with another tobacco that is already extremely moist. You can mix it with an identical blend that is plenty moist, always making sure that the dry stuff goes in in small quantities so that you don't dry out your good tobacco too much. I have done this in the past with some Dunhill Nightcap that I had let get too dry, by simply adding it into a new tin of Nightcap.
In the last couple of weeks, a side-effect of my mixing Gray Ghost with Perique has been to rehydrate the Gray Ghost. I have purchased straight Perique from two sources: C&D and Cup O' Joes, the latter of which is McClelland's brand Perique, and is the version I am using at present. Both versions have been quite extremely moist. So moist that it has tended to balance the overall moistness between the GG and Perique quite well.
This method of rehydration may be something to keep in mind next time you have some tobacco that has gotten too dry.