As a coward speaking about something he knows very little, here is my two cents worth.
Coward because anything can be fit to anything given enough time and effort. So the initial answer is yes, you can install the 2000 seats in the 1999. If the question is "How easy is it?" my answer is I do not know.
From experience, not with Taurus but with a 1981 Ford Escort, you can install any seat into anything. The 1981 Escort seat was notoriously fragile. With a gravitationally challenged body, I broke the seat back. Said seat was removed, welded and reinstalled. A decade later it broke again.
This time wanting to update the interior a bit, I bought a set of newer buckets from a wrecked Mustang ($50 for the pair.) All we kept was the seat base (the part that bolts to the floor) while the rest of the hardware (slider) came from the Mustang. It fit, had slightly longer travel than the original and felt fantastic.
My son's friend swapped the entire interior out of a Focus SVT into a Focus ZX3 (identical bodies) in less than a day (we are in the process of swapping the running gear out of the same SVT into a Focus wagon).
With both cars side by side, I would measure the passenger side seat mounting holes and compare. Measure the seat height and compare. Odds are the distance and location is the same. If there is a difference, check underneath the seat to see if the slider will fit the base. Again, a tape measure is your friend (that is what we did to swap the Mustang buckets into the Escort.) The rear seats are a different matter entirely. Wagon rear seats fold down. Not sure about the sedan.
So the fool in me says go for it. Until you burn the old seats, everything is reversible.
It will all bolt in properly. Best way (installed 96 SHO seats in my 2000) is to remove that rubbery/plastic grab handle to adjust seat back tilt. Check under topic finder for seat dissassembly. Either two approaches...one you use the 99 seat metal bases, or the 00 seat bases...depending on who has power seats, etc.