There are accounts that was tagged as out of scope and need not to be used in an opportunity.
But we cannot set this as inactive since we still have remaining transactions.
You can have lookup filter for Account lookup on opportunity in such a way that those accounts are not allowed to select while creating opportunities. Lookup filter can be either on record type or name or any other field.
Create a Checkbox field On the Account Say it Out Of Scope
Solution: - create a Validation Rule on Opportunity.
AND( NOT(ISBLANK(AccountId)), Account.Out_of_Scope__c )
Display the Error that Opportunity Can not be created on Out of Scope Account.