>Without knowing more detail on the layers it's hard to say. But I'd be inclined to leave the base class alone. If you do that you could simply add an additional method to the child class. So given an implicit cast to 'ShortOperator' you could just add a method:

public IEnumerable<ShortOperator> GetAllShortOperators()
> {
>     return  _operatorRepository.GetAll().Select((x => (ShortOperator)(x)));
>  }

I got this

public IEnumerable<OperatorList> GetAllOperatorsList()
        {
            return _operatorRepository.GetAll().
                Select((o=> new OperatorList{ OpCode = o.OpCode, 
                    FirstName = o.FirstName, LastName = o.LastName, 
                    Hidden = o.Hidden, OpCodeHash = o.OpCodeHash })
                           );
        }

but not sure how to create a similar method for PagedResult

 //public PagedResult<OperatorList> GetOperators(QueryRequest queryRequest)
        //{
        //    return _operatorRepository.GetPagedRequest(queryRequest).Select((x=> (OperatorList)(x)));
        //}

as GetPagedRequest doesn't have Select method.