Changing GL master Records

I need your help for the following scenario:

Client needs to change the GL master records to make them into reconciliation account for vendors.

Facts

- All of these GL accounts have posting

- Some of these GL are open item managed while others are not

- All of these are balance sheet accounts

- All of the GL accounts have ' Only balances in local currency' ticked

For GL accounts which are open item managed, I posted a clearing entry into a clearing account, reducing the balance to zero ( in document, local and group currency).

However, when I try to change the settings (FS00) of master record, the system returns the following messages:

- Changing the balances in local currency not possible; acct has a balance

- Changing the reconcil.acct indicator not possible; acct has a balance

The same thing happens when I tried changing the settings for GL accounts, which are not open item managed.

Request you to share your expertise in this context.

Note: Client is not interested in using another GL account because of the way the reporting is structured.

Thanks & Regards