Quote from: Sanglotslongs on Today at 07:08:51 AM

Is it good security practice to use custom parameters above ?

Things like this are never considered "security practice" if you ask me. They are false sense of security.

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Even if you forget them, you still have your mnemonic seed and will be able to bruteforce address and PBKDF2.

If you can do it, the attacker can too.

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It can make your mnemonic seed more secure if someone stole it from you. Give you time to move funds etc.

The thief is not going to leave any traces behind and if they can gain access to a hard copy of a mnemonic (assuming it is for a cold storage and stored the "right way") it is safe to assume they know more about you than you think.

If you want to modify the algorithm them why stop at such a simple change and not make a better change that can actually give you a proper security?
You have a mnemonic that is n-bits (eg. 128-bits for 12 words) take those bits and encrypt them with AES256 with a key derived from a strong passphrase and a salt derived from the address (like BIP38).
Now you get 128-bits of encrypted data (encryption without IV) which you can encode to 12 words using the same BIP39 scheme. All you have to do is write down these words as if they were your mnemonic.

To import to a wallet you just decrypt these words and convert to an un-encrypted BIP39. That is decode 12 words to get the byte[], derive the AES key from the passphrase and address like above, decrypt using AES256. Now you have un-encrypted 128-bit entropy. Encode this using BIP39 scheme and you have the original words.