Automatic Generation of Appropriation Request (AR) in the transaction IMA13

Hi,

I am creating the C type Appropriation Request (AR) in the transaction IMA13 (IM).

The requirement, "AR number should be generate automatically by picking some values (Combination of subclass and Fiscal year) in AR, which are entered by creator".

Here, I need to overwrite the system generated AR number (default) with this automatic generated AR number.

There is BAdI (APPREQUEST_UPDATE) available to check the Appropriation Requests, but it is not having any exporting parameter to export the automatic generated AR number.

Could you please, help me in this....?

Thiru