unlikely coding will be required if youre only replacing the exsting speakers with the same impedance. Upgrading just the existing speakers with 2 or 3 way half decent aftermarket will give superior Dynamic sound and dynamic range with crisper clear sound.
Admitedly it won’t sound as good as a system with 10 speakers, amp and sub, but it would sound better than bargain basement speakers fitted as standard to lower spec car’s, plus your hardly going to notice.