Every Formula 1 team may not use more than two racs at any one time during an Event.
Spare cars are not allowed, but teams may bring additional chassis which can be built up if a race chassis is damaged beyond repair.
Any drivers who uses another car or whose car had a change of survival cell following the third practice session must start the race from the pitlane.
After the start of the race, no change of car is permitted.
FIA F1 2017. sporting regulations can be downloaded here.