In a situation where the number of values to exclude is high, and there is no rule, I'd rather keep the values to exclude in a separate data soure (database table, flat file). This will allow to create a field of the "not-excluded" values in addition to the field with all values. Although you say you don't want to do it in the script, this is the best way. A compromise is'to use flags based on the same data source of the excluded values, but I don't see why I'd do it if I'm changing the script anyway. The only way to avoid any script changes is a calculated dimension with set analysis where you list all values you want to exclude. I do not recommend creating suc a monster.
AB, AC..........AZ Values as Prod id. I have excluded M & N Values in the Load script.
I needed A& B values in Sheet1 and have selected only A & B value of Prod ID using expression field . I have selected B & C using Expression in Sheet 2. Now i want to exclude A to Z in Sheet3 and have rest (for example AA, AB..... ZZ)