hi Yogesh
in OBD2, Maintain field status group account management - Company code data , the reconciliation account even if you would have maintained the AKONT as required field you can change it if you have correct authorization object, this has nothing to do with changing the AKONT field,
I have made my recon account as reqd in OBD2 still i can change the recon account in Customer master data, so I hope it is a authorization issue only