I didn't see any repair guides yet so I thought I'd make this up.
To start off with, this method may NOT completely repair a cracked wrapper. It depends mostly on where the crack is on the cigar. If the crack is on the body or the foot, this will prevent the crack from spreading up the wrapper if the cigar begins to swell a bit when smoked. If the crack is on the head, it will repair it to the point where it will allow you to smoke a cigar that might otherwise be unsmokable. If you're a wet smoker, your saliva will break this pectin down. In the case illustrated below, the cigar might have unraveled once the head was cut. This repair allowed me to cut the head and begin smoking without any problems.
So you've discovered that one of your cigars has a cracked wrapper. This can happen in a couple different ways. For me, it seems to happen more often when you order cigars that come in slide lid boxes also known as cabinets. It shouldn't be a common occurrence and if it is, you should probably look for another vendor. To lower your odds, you should ask that the box be opened and inspected by the vendor. I, however, like the idea of being the first person to break the seal and see, touch and smell the cigars since they left the manufacture so I generally ask that my boxes remain sealed. The only time I request that they be inspected is if the box is older than 2 years old. Why 2 years? I have no idea. It's just a number that I came up with.
So, why not just take the cigar back to the shop? If you got it at a B&M, that is an option. But if you've left the store, there's a decent chance they'll tell you to pound sand. If it's just 1 or 2 cigars from a box, to me, it would just be easier to fix the cigars and smoke them and not bother with returning the box for an exchange. If the entire box is damaged, then I would certainly contact the vendor and setup an exchange.
What you need: Cigar Glue
Or make your own.
Notice the very small amount of water in the bottle cap. Mix in a little of the fruit pectin with the water in the bottle cap. You don't need much but you'll want it to completely dissolve. I don't bother measuring. If it won't dissolve, just at a touch more water. It'll be a gel like consistency and clear. I usually just use my finger but you might find a toothpick to be handy.
You can find fruit pectin in any grocery store around the canning section.
Here is the problem cigar: Cracked head through the caps and a fairly severe crack at the foot. The problem here is the crack at the foot is likely to spread up the cigar as it's smoked. Cutting the head would likely cause the crack to spread and the cigar will begin to unravel since the crack goes through the caps.
Again, if you try and cut the head of this cigar, more than likely the crack will spread down the cigar and since the cap is already split and the cigar will immediately begin to unravel. That is no bueno and ruins the experience of the cigar. If you do move forward to smoking without addressing the cracked foot, there's a chance of the cigar swelling a little and the crack spreading up the cigar as you smoke. Again, that's no good.
So you just dip your finger in the pectin gel (or toothpick or whatever tool you want to use), and spread some of the pectin gel over the crack. If you can get some under the crack between the wrapper and binder, that's preferable but if not, don't force it.
Just leave the cigar out and allow just a few minutes to dry. I let this one sit for around 30 minutes.
I didn't take a picture of the foot because I didn't attempt to glue the gap closed. My goal was only to prevent it from getting worse.
Here it is cut. For those who care I used a Xikar Xi3. The important thing here is the wrapper and caps stayed together and aren't falling apart. That was the main goal.
Here you will notice that the cracked foot did not spread up the cigar. Also, my saliva is starting to break down the pectin glue. Again, this repair has it's limitations but we're still good. (ARFCOM obligatory feet in the picture)
Here's the last picture. It was only around this point where the head was starting to come apart to the point where it was unmanageable. I was able to simply slide the band up a little to hold everything together for the last 10 minutes or so before I laid it down.
That's it. Easy peasy.