Disable Account usage for system intercompany accounts

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Hi 

We have a scenario where we want the intercompany accounts to be disabled from manual or user posting . We do not want user to select the account & only have system post the balance. 

One option is to use the security rule to restrict the account usage , however this would cause the account to not show up in FR reports which is an issue . We need to disable only the account usage from manual entry and not from reporting 

Any suggestions 

Thanks

Rohan