The one big thing you need to watch out for when moving code from one PIC to another is how the registers are configured. You need to go line by line and look up registers. For example, maybe timer1 one is associated with CCP2 on one chip and CCP1 with another. That is just purely an example but things like that are common. It might be the smallest difference from one PIC to another that will prevent code from working on one and not the other.