The attacker has the source of TrueCrypt just like you, and thus can remove that kind of limits and brute-force your password.
The crackers may be able to alter the truecrypt source on their own machines but I don't see how you are proposing they can alter the code on an already encrypted volume.
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Funny but the general idea behind encryption in the workplace is to guard against the theft of a laptop, not the theft of a laptop and an employee.
The attacker has the source of TrueCrypt just like you, and thus can remove that kind of limits and brute-force your password.
The crackers may be able to alter the truecrypt source on their own machines but I don't see how you are proposing they can alter the code on an already encrypted volume.