1. Place ham in slow cooker, pour in pomegranate juice, cover and cook on low until completely warmed through, 4 to 6 hours, basting once or twice. Put jelly in a small saucepan over medium-low heat and cook, stirring, until softened. Pour through a fine-mesh sieve into a bowl, discarding solids. Cover and refrigerate jelly until ready to use.
2. In a small saucepan, combine 3 Tbsp. of cooking liquid from slow cooker with jelly, mustard and brown sugar. Bring to a boil over high heat, stirring until sugar has dissolved. Remove 1 cup of cooking liquid from slow cooker; discard. Pour jelly mixture over ham. Cover cooker and increase heat to high. Cook for about 30 minutes, basting often, until shiny and glazed. Transfer ham to a platter and let stand at room temperature for 15 minutes; serve.