From November 1853, engineer Sylvestre du Perron directed work on "Souverain" to add a 600-shp steam engine, after plans by Dupuy de Lôme, without lengthening the ship; "Souverain" started her new trials in June 1857, under Commander de Jouslard. In her new configuration, she still carried 110 guns. In 1862, she was reconfigured as a troopship for the Second French intervention in Mexico, with only 16 30-pounder long guns, under Captain Sévin. "Souverain" was listed in the reserve between 1863 and November 1866, when she took part in the French retreat from Mexico, under Captain Leblanc.