Remove Rear Armrest (Center)

I think the experts will disagree with you. That is why the restraint fasteners are behind the driver seat and passenger seat.

Dont know about the 2012, but if you look below you will see similar threads.

 

Have you tried placing the carseat in the center and see if the center armrest falls down? I doubt it. With the carseat pressing on the center armrest, the armrest will not fall down by anymeans. If your assumptions are true, most vehicles won't have any center armrest and I'm talking not for the just prius alone but for a good number of other car manufacturers.

 

Here's the instructions, but I agree with ImeanGreen, you shouldn't have to do it.

 

Fold down armrests are not a problem for carseats, even rear-facing ones, unless specified in the vehicle or carseat owner's manual. Generally, you will not find any type of restriction about fold down armrests.

Some older Evenflo seats did have such a restriction, but Evenflo removed this instruction many years ago.

Rear-facing seats are inherently very safe, especially in side impacts. While the center seat has shown to offer an advantage in side impacts, this is based on older studies with vehicles made before side impacts were a priority in vehicle or carseat design. With today's vehicles and carseats that have much improved side impact protection, there is little issue placing a rear-facing child restraint in an outboard seating position.

There are some other reasons to choose center or outboard seats. In Toyotas, you generally cannot use the LATCH position in the center. Plus, the outboard seat tends to be easier for loading and unloading. On the other hand, the center seat generally gives more room for a rear-facing carseat as the back will fit between the front seat backs to some extent.