I am pleased to learn (thanks, Wikipedia!) that there exists a sequel, 0'00", a.k.a. 4'33" No. 2.:
In 1962, Cage wrote 0'00", which is also referred to as 4'33" No. 2. The directions originally consisted of one sentence: "In a situation provided with maximum amplification, perform a disciplined action." The first performance had Cage write that sentence.
The second performance added four new qualifications to the directions: "the performer should allow any interruptions of the action, the action should fulfill an obligation to others, the same action should not be used in more than one performance, and should not be the performance of a musical composition."*