Can you replace rod bearings with engine still in car?

I say, NO. Yes, you can crawl under there, get "all oily" and get the bearings out and back in.

But that does not make it RIGHT

If the rod bearings are worn, the crank probably is, too, and some of the rods may have been "pounded out."

I say, if an engine needs rod bearings, it needs to come out

Inspect it, clean the oil system out, mike the entire crankshaft, mains and rods, and go from there. Pull the pistons / rods and have the rods checked (minimum) for out-of-round, I.E. have them reconditioned.

In this day and age, unless an engine was really run hard, as in raced, the rod bearings should last as long as anything else, generally speaking. So the question IS, "why just the rod bearings?"