Rent paid details not in form 16.can it be deducted in itr1?

Hi,

       I have  filed a return in which the employee had not given House rent paid details to the company. So while calculating TDS the company has not adjusted HRA exemption. Therefore it is not coming in orm 16 as well.

                             I got an advice that as far as salary is concerned Form 16 details can not be altered. So I filed the return yesterday acccording to the form 16 without claiming HRA exemption. 

                               Today I got another advice that eventhough the exemtion for HRA is not calculated by the company we can deduct the allowable amount while filing return.

Kindly advice me on the following points.

1) Can I deduct HRA allowance in the ITR 1 eventhough it was not deducted in Form 16?

2) As in ITR 1 there is no option to show HRA exemption specifically can I simply deduct it from total salary income given by the company as per Form 16 and show the salry after adjustment of HRA excemtion in income from salary column?

3) As I have already filed the return yesterday can I file a revised return today? If I file the reviced return should the employee should send both the acknowledgement to the income tax dept.or only the revised return?

Kindly advice

Note : I am doing online filing