MB21/MB22/MIGO - change account assignment (GL ACCOUNT)

HI,

Sometimes users make mistakes and use the wrong GL account when creating reservation in MB21. Once the reservation is saved, it is impossible to change the GL account field content in MB22.

Is it possible to configure this field so it can be changed ? I looked at screen layouts in IMG but it does not seem possible.

Is it possible to configure SAP to that the GL account field is changeable for the good issue (MIGO)?

Thanks.

Julien