A Java GUI for hacking Candy Crush save game files
If you do not wish to compile this yourself, the binary can be found here
To run this program you will need access to your save game file. This is easily acquired through various methods.
I'd recommend iFunbox if you're on Windows. Connect your iPhone to your PC and open up iFunbox. For what it’s worth, I prefer to use the application’s classic interface – it just seems more straightforward. Navigate to User Applications > Candy Crush > Documents as shown below and copy the save_##########.dat file to your computer. This program automatically creates a back up at in the same directory as your save game file (just with .bak appended). (credit to geek-republic)
If you're on a Mac, I'd recommend iExplorer. Follow the procedure above.
I leave it as an exercise to the user to go more in depth than this - if you really need more help, google around for a few guides or check out /r/jailbreak on reddit and ask for help there. Should be fairly trivial to get the save games off/back on your device, though.
This is confirmed to work through iOS 10.2 on December 21st, 2016.
One final note - your lives get reset after every level you beat. The rest are persistent, though.