I booked a fast train from Florence to Rome and want to know if there are any stops along the way. If so, is it possible to get off then back on later that day without penalty or rebooking.
Go to the website where you purchased the ticket and click the arrow to expand the view; it will show you if there are any stops. However, if you've booked a fast train, you will have a reserved seat so the ticket is good only for that train/that time/that seat. So even if there's a stop, you can't get off and later reboard on the same ticket. Even with a regional (slow) train, I don't see any way you could get off and later reboard another train with the same ticket. Before you board, you need to stamp the ticket, which shows time. I don't think it would be possible to reboard later, with a ticket stamped many hours before. If you want to stop, buy separate tickets.
with a fast train there are no stops between Rome and Florence.
Most of the fast train runs are non-stop. If you want the option of hopping off and hopping back on, you need to take an all-Regionale train run. Your train journey time will double as you are on slower trains that make every stop along the way. When you buy a ticket on the Regionale train, it will show point A to point B. In this case - Florence to Rome. Unlike the fast train tickets, this ticket is good for 60 days. No specific train, travel date or travel time. No seat reservations either. You just validate the ticket, get on and find your own seat. You can get on any Regionale train during the 60 day period making the run shown on the ticket. When you validate this ticket with a date and time stamp, the ticket is now good for 6 hours which exceeds the time for any Regionale train run. If you want to hop off and hop on, you could do this as long as you finish the journey shown on the ticket within 6 hours. Or, better yet, pick a location that you would like to visit (i.e. Chiusi) and buy two tickets. One from Florence to Chiusi and one from Chiusi to Rome. Just don't validate the Chiusi to Rome ticket until you've done with your visit and you are ready to get back on the Regionale train. Since this is something you want to do, you might want to hop off at Orvieto.