Can a thrust bearing be changed with the engine in the car? (318)

I don't see why not, except there's a lot holding those shells in place. There used to be a little "tool" (you can make one) All it consists of is a little smooth rounded stud which you put in an oil hole. You line it up with the edge of the bearing shell, wrench the engine over gently, and the tool forces the shell to "rotate out."

I would GUESS in some cases you might have to loosen all the mains a little to allow a little more room in there