客串的英文说法

to be a guest performer;
to appear as a guest on a television or radio program;
(Am.) to guest

客串 [简明汉英词典]
be a guest actor
[(an amateur) plays a part in a professional performance;be a guest performer] 专业剧团临时邀请非专业演员参加演出;也指非本地或非本单位的演员临时参加演出

guest performance