I think since he bought the licence there is no-one to sue him for forgery or something like that. Quite possible the artist didn't only write directions on how to create the artwork (e.g. the kind of tape, the direction of the tape, the orientation of the banana etc), but also 'rules' on what not to do with it. If he would expose this work different the artist could possibly sue him for breaking their agreement.

There is an artist (Sol LeWitt) who is famous for instructing others to create his work. He didn't sell the artwork, he sold the exclusive right to follow a set of instructions. Quite interesting work also, here is a link:

In 1968, Sol LeWitt began creating his wall drawings, which consist solely of written instructions and diagrams for others to execute. LeWitt likened his instructions to musical scores, which are realized in a new way every time they’re played, and it’s possible for LeWitt’s wall drawings to take slightly different forms, depending on how his directions are implemented. Although the idea of the work is meant to be preserved, the work itself is often ephemeral, and it can exist in more than one place at one time.

https://risdmuseum.org/manual/45_variations_of_a_drawing_sol_lewitt_and_his_written_instructions

He died in 2007, but there still are exhibitions of his work (the execution of it of course). Worth going if you get a chance.

I dunno, maybe if you never put it up again. But you could also think of it as a performance where the act of putting up and taking down the banana is part of the art. And the person who "owns" it gets to be part of that, which is special.