You can shift from 2h to 4h on the fly up to 35mph. Most, if not all pathfinders came with auto locking hubs. You would need to come to a stop for the auto hubs to completely disengage, but it won't hurt anything if they are always engaged. Once the transfer case lever is shifted back to 2H the transmission is completed disconnected from the front differential so there is no chance of damage even with the hubs engaged.. Shifting from 4H to 4L requires that you be stopped with the transmission in neutral.