When a developer changes the name of an application, does the old one become available?

I wrote an iOS application and would like to call it "X", but this name is accepted. The existing application is not very popular, and the author is ready to rename it for a fee. Suppose we agree to do this, does the old name become instantly accessible to everyone, or does Apple keep it as inaccessible for some time, perhaps forever?

If the old name is locked forever, does Apple allow me to simply buy out all of its application (he wants) and then publish completely different content using the same name and application identifier? We may need to change the category.