Yes. Keep in mind whenever you leave a covenant you effectively "lose" half of the items that you have offered to increase your rank. Example: You've offered 10 dragon scales to get to covenant rank +1 and you leave. If you were to rejoin, you would be rank 0 and it would be like you had only offered 5 scales. Offering another 5 would renew your status to rank +1. If you offered 80 to get to rank +3, leave and rejoin, you will be rank +2 and have to offer another 40 scales to get back up to rank +3. Also, although you can use the Dragon Head Stone and Dragon Torso Stone even while you are not a part of the covenant, you will not have access to any of the rank-based enhanced effects as long as you are not a covenant member. When you rejoin, whatever rank you are then dictates how effective those skills are.