He changed his name to Taneyasu from Tsuneyasu, when he was granted to use a portion (in this case 'tane' written in Chinese character 稙) of the real name of Yoshitane ASHIKAGA, the 10th Seii taishogun (literally, "great general who subdues the barbarians") of Muromachi bakufu (Japanese government headed by a shogun).
室町幕府10代征夷大将軍・足利義稙の偏諱で恒泰から稙泰とした。