It seems like making session variable UserID(for member discount) in Powerstore is indeed a little more complex like you said. I'm looking for the less complex way to achieve a result where user logs in order to receive the discount. Can I achieve this like you pointed out by setting the session variable on the login page using RegUserID? Then just create the user discount rule, Condition and Amounts ?
In either case scenario way (complex or not) do I (this might be an absurd question) to still create(add) two new columns in powerstore? ( like for MemberPrice, Current Price) . what's your tip?