The word mudaseis is the imperfect subjunctive form of mudar in the second person plural.
See the full mudar conjugation
Me alegro de que os mudaseis a Nueva York.
I'm glad you guys moved to New York.
Sabeis, estoy contenta de que os mudaseis a la puerta de al lado.
You know, I'm glad you guys moved in next door.
Sabes, hay una forma en la que no tendría que decirle nada a Casey... si tú y Ben os mudaseis aquí. No.
You know, there is one way I wouldn't have to tell Casey anything... if you and Ben moved in here.
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