If someone was in school full-time as an F-1 student, he can apply for an OPT to get an employment authorization document. Anytime before or after OPT a foreign national can change his or her status to a different nonimmigrant status, such as Tourist. An extensive explanation must be made what the student indents to do as a tourist, and, most importantly, the availability of funds to cover the tourist activities must be shown.
One important note: before applying for a new status, an applicant must be eligible to it. The the petition must not be “frivolous”. Some applicants request a change of status to dodge the inadmissibility bar and to “win” more time. Usually, it is not a good idea.