1996 Mercury Sable replacing coolant resevoir

Surprisingly no, remove the screws and hoses, remove the old resevoiur and reverse with new part.
I would suggest parking a slight incline to aide in purging air from the system when you refill it.
Fill the system, start engine with cap off of resivoiur and run for a few minutes, shut engine off, let sit for about a 1/2 hour to cool and pull fluid back into system, top off if needed, replace cap and you are done. I do recommend checking the fluid daily for the first week and then every 3 - 4 days for the next month, just to be sure. After that I do recommend checking all fluids at least once a month as a regular practice.
Hope this helps, let me know.
Dan