It's better to modify your site to accept only modified usernames/email adresses (e.g you must always login by adding a - to your username) for the user account

It's better to modify your site to accept only modified usernames/email adresses (e.g you must always login by adding a - to your username) for the user accounts that are more important (has more rights) then normal accounts. A hacker will have problems bruteforcing these accounts..