Hi,
Actually why client want to remove check of line item display tick from the reconciliation account ? as if they remove tick they cannot view document wise display details for that vendor.
In case you want to remove tick you need to Open one more G/L and transfer all balances to the same through transaction code F-30 and selecting option Transfer with clearing.
Once balances are transferred clear earlier G/L through F-30 transaction.
Regards,
Tejas