I've been trying to understand Bitcoin better, and I've got some questions about nLockTime and RBF. From my understanding, nLockTime is like a delay timer for transactions, and miners can't confirm them until the set time is reached. RBF lets you replace an unconfirmed transaction with a new one that has a higher fee. Also I understand that transaction with nLock time set can be replaced by a new transaction with RBF feature so far the set time is not yet reached and has a higher fee. I'm okay with that but I have two questions:

1. Can a transaction with nLockTime be replaced with a new one that has a different nLockTime value? What happens if it gets replaced?
2. If a transaction with nLockTime is stuck in the mempool because of low fees, can I use RBF to replace it with a new transaction that has a higher fee?

I for ask this question for main board but sometimes their explanations and terms used de dey too complex for easy understanding. Hope person fit help clarify this for me here.