Trial and error is theoretically possible because an .mpr file is SQLite-based, but in practice it’s very risky since Mendix’s internal model structure is not documented and it’s unclear which records are safe to modify. A wrong change can easily break the project or cause data loss.
Therefore, sending the file to Mendix Support is the safest approach, as they have internal recovery tools. Before doing anything, always make a backup of the .mpr file to avoid losing the only copy.