Is it good security practice to use custom parameters above ? Even if you forget them, you still have your mnemonic seed and will be able to bruteforce address and PBKDF2. It can make your mnemonic seed more secure if someone stole it from you. Give you time to move funds etc.
If someone stole them from you, and they didn't know that you changed the custom parameters, it'd be a matter of time until they access your funds. It would surely be more secure since it'd require more computational power for the attacker to successfully find it via brute force, but if you forget them, so do you. You may also are unaware that someone compromised your room and found your phrase. The purpose of the seed would have already lost its point.
Why don't you simply use a strong password if you're afraid that they may break into your place? It isn't that hard to pick a long password that provides you more security than a bunch of additional PBKDF2 iterations.