Choose your substitute by goal: closest overall flavor (paste-based) vs fast emergency heat (chili pastes).
Use the listed ratio relative to your original green curry paste amount, then whisk into a little coconut milk (or water) before adding to the pot.
For curry powder-based swaps, bloom in warm oil 30–45 seconds to activate spices before mixing with coconut milk.
Adjust the finish: add lime juice/zest for brightness, a pinch of sugar to round chili edges, and salt to match the original curry’s savory balance.
Simmer 3–5 minutes so the aromatics integrate; taste and correct heat/herbiness last.