It is likely they will charge you either way, the shop has to make sure the system is working when the vehicle leaves, per federal law.
Just do it yourself and save all of the money.
This is not true, read below!
1. If the customer comes in with a malfunctioning sensor that cannot be immediately replaced, can the shop temporarily replace it with a snap-in valve stem and return the car to service?
According to NHTSA, "a motor vehicle repair business would not
be violating 49 USC 30122(b) by removing an inoperative or damaged TPMS sensor and replacing it with a standard snap-in rubber valve stem.”
"This is exactly why our training programs have always stressed the importance of checking the status of the TPMS prior to service," said Kevin Rohlwing, TIA senior vice president of Training. "If a valve stem sensor is not functioning prior to servicing the tires and wheels, then the retailer cannot violate the "make inoperative" provision because the system was already inoperative. This increases the importance of documenting an inoperable TPMS prior to any work being performed on the vehicle, especially now that the batteries in the sensors are starting to die." This is pretty straightforward; if the sensor is already malfunctioning when the car comes in, the shop can do what is necessary to keep the car running. However, there are some further questions as to what exactly constitutes “inoperative” when the customer comes in. I'll address that further below.