Hi Kiran,
For any account assignment object to be displayed in AA master data, the posting key 70/75, screen layout of asset should allow in field status.
if cost center and business area remain the same , then these can be defined as time-independent objects.
if in ACSET, the objects are marked as balance sheet, then system wont allow to change the values once asset is capitalized.
For the current issue, need to check the field status of posting keys and screen layout of the asset class for business area field.
Cheers,