Restricting Main Sales Account Account in Receivable Module for passing Manual Transaction.

Hi,

We do not want users to use on specific account, Our Sales Account, in Receivable Module  to pass manual transaction of Credit memo or debit memo.   it should be   used  while creating Invoice using Interface from externaL Source or Sales Order Invoice from Order managment.

In our Auto accounting Rule we have given the option of defaulting Account segment from Customer site. When we craete customer we are giving Sales account at Customer Site level, which is defaulting when user passes manual  transaction.

I Tried to use Sceurity rule to restrict the same but the entire revenue account segment is getting greyed out  and not able to chage it some other account.