Unfortunately, you can NEVER rely on what an underpaid, unmotivated, disinterested airline employee tells you on the phone. They rarely know the airlines policies, and frequently don't even bother to look up the information before telling you what you want to hear just to get you off the phone. You must ALWAYS find the information on the website, print it and carry with you if you have any questions about policy. Often, the airport agent won't know or look it up either. They'll simply say "no, it can't be done", so you have to be prepared. Try contacting the Director of Customer Service at Spirit.
www.heather.harvey@spiritair.com Good luck.