you don't have to replace the bolts. if your thermostat lifts out , it won't take 15 seconds to replace it with the new one and you won't lose a lot - maybe a pint of coolant. if you take longer, you might lose the contents of the reservoir but not much more. when you take off the housing just make a note of the thermostat's orientation to avoid putting the new one in backward.
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"