Hi
Your question is not very clear. Are you talking of New GL Migration or legacy transfer of balances or S/4 HANA Finance migration.
If you are talking of Legacy balance transfer, we generally upload only the balance even if the GL is line item managed. Of course, if you are loading balances at account assignment level like profit center or segment say in a New GL Enviornment, you may have multiple line items for a GL Account which means that there will be one line for each account assignment for that particular GL Account.
Regards
Sanil Bhandari