I assume a cap subject H-1b petition was filed for you, and approved for an October 1 start date. If that is the case, and you begin working on October 1st when your status changes from F-1 to H-1b, then you could change back to F-1 (with a new I-20, and either a change of status application, or a new entry with an F-1 visa). When you finish your program, an employer could file an H-1b petition for you based on your new degree, with an appropriate job offer. You would not be subject to the...