Can you have a Property as a line item in a module by the Account dimension for 4* ,5* and 6* to be classified into respective groups. Say Account category. You could also use left(code(account),1) to determine them using a formula and assign the account category using a formula.
This will only work if you want to sum up all accounts that are in 4, 5 and 6 and not sum them seperately per account category. If you want to sum them seperately you would need line item per category. Then if you want to show these figures in different modules, you would need to create 3 additional line items per value you want to show. Moreover, even though my suggestion (/Arun's) requires more time now, it will not require additional time when categories change. So which you implement really depends on what you want to do with it in the end.