Using a square of cheesecloth, make a spice bundle: Place thyme springs, juniper berries, bay leaves, and black peppercorns in the center of the cloth and secure with kitchen twine.
In a slow cooker set to low , arrange pork roast in the bottom. Add water, spice bundle, and salt.
Cover and set for 10 hours. It may take 12 hours, carnitas will be ready when pork is easily shreddible with a fork.
Using a large slotted spoon or a pair of tongs, transfer pork to a large bowl (save cooking liquid for later). Allow pork to rest, covered, for about 10 minutes.
Heat taco shells according to manufacturer's directions, and prepare toppings of your choice.
Shred pork using two forks or tongs, discarding excess fat. Taste cooking liquid. (if it is too salty, thin the cooking liquid with hot water). Moisten carnitas with 1 cup of cooking liquid, reserving the rest for later use.
Fill Taco shells with Copycat Chipotle Carnitas, and desired toppings.