Key Features:

1. Manual Exchange Rate Toggle — An Enable Manual Exchange Rate boolean toggle is added to Sales Orders, Purchase Orders, Invoices/Bills, and Payments. It only appears when the document currency differs from the company currency, keeping the interface clean for same-currency transactions.
2. Per-Document Custom Exchange Rate — When the toggle is enabled, a high-precision (12,6 digits) Exchange Rate field appears, letting users override the system-default rate on a document-by-document basis for complete control over every transaction.
3. Auto-Populated Rate (Smart Default) — When the toggle is first enabled, the rate field is automatically pre-filled using Odoo's live currency conversion engine as a convenient starting point — the user can then fine-tune it to any desired value.
4. Seamless Invoice Inheritance from Orders — When an invoice or bill is created from a Sale or Purchase Order, it automatically inherits both the manual rate flag and the rate value from the source order, ensuring full rate consistency throughout the order-to-invoice flow.
5. Payment Rate Override with Accurate Journal Entries — The manual rate flows through to the Payment and Payment Register wizard. Journal entry line balances (liquidity and counterpart accounts) are recalculated using the custom rate, ensuring correct debit/credit amounts in company currency.
6. State-Aware Read-Only Protection — Rate fields automatically lock once a Sales or Purchase Order is confirmed, or once an Invoice is posted — preventing accidental rate changes after a document has been approved.
7. Auto-Reset on Currency Change — If the document currency is switched back to the company currency, the manual exchange flag is automatically reset to off, keeping records clean and avoiding stale rate data.
8. Full Audit Trail via Chatter Tracking — All exchange-related fields carry change tracking on every model, so every rate modification is logged in the chatter with user, timestamp, and old/new values for complete audit history.
9. Broad Coverage Across All Financial Documents — Manual rate support spans the entire financial workflow: Sale Orders, Purchase Orders, Customer Invoices, Vendor Bills, Payment Register wizard, and standalone Account Payments.
10. Lightweight & No Extra Dependencies — Relies only on Odoo's core modules (base, account, sale_management, purchase) — no third-party libraries required, ensuring easy installation and long-term maintainability.