If you need developer-level customization, WordPress hooks are still the safest extension point in version 3.x.
In general, PHP hooks are more stable across versions than old frontend DOM assumptions or legacy jQuery integrations.
- See how to change the calculated price
- See how to enable or disable price formatting
- See how to add advanced validation rules
- See how to show or hide the calculator
For frontend-only changes, first consider theme options and scoped CSS. For JavaScript integrations, see JavaScript integration.