As per the law, Form 67 is required for claiming Foreign Tax Credits by an assessee and it should be done along with the return of income.It is possible to file Form 67 before filing the return.The question is whether the Form can be filed after filing the return of income. While the requirement is procedural, a return may be termed as incomplete if the form is not filed along with the returns and an officer can deny foreign tax credits.However, for all intents and purposes if you file Form 67 before the completion of assessment or even with an application u/s 154 once the assessment is completed, it cannot be denied if the facts have been already disclosed in the return and teh form in itself is only completing a process.However, to avoid adventures with the department and unwanted litigation, it is always prudent to file the form with the return of income so that it is not missed out or forgotten.