-snip-
Each time you want to make a transaction, there will be an option to flag a transaction to make it support RBF, but the latest electrum starting from version 4.1.1 and up, the transaction will be automatically support RBF unless you flag it not to support RBF.
-snip-
It has been turned on by default for quite some time, since one of the version from 2018.
This is the way to cancel a transaction too, the fee will be pump but the address will be changed to another address on the wallet so that the unconfirmed bitcoin transaction will be diverted from the former receiver's address to another address which is from the sender's wallet address, which means the transaction is cancelled but require higher fee.
Almost there. Even if you were to use RBF and spend the inputs to another address, miners can still choose to include your first transaction instead of the one with the increased fee. They are both valid until one of them gets confirmed.
In all cases of RBF, there will be change of transaction hash (txid) as the unconfirmed Bitcoin is double-spent.
It is changed due to either some change in the inputs/output or some change in the value of the outputs.
No offence, the post is actually extremely wordy and some better structuring would be needed.