Well, good news is the new infrared sensor worked! I swapped it, put it back together, plugged it in, turned it on WITH THE REMOTE!! and.... big black line going through the screen.
I mustve damaged the screen and put a little too much pressure somewhere. Theres no obvious damage like cracks or wire shorts but theres so many complex, fragile connections in these ribbon connectors that Im sure whatever I did cant be fixed. (At least not for any reasonable cost.)
Moral of the story is yes, you can swap out the IR sensor and I resolved that issue quite easily and got the remote working. But I learned a lesson to be more careful next time I'm delving into the innards of a TV. A frustrating lesson but to be fair my next solution was to just buy a new TV anyways.
Now I've got an extra IR sensor laying around in case another one goes out. Maybe I'll put it back on Ebay for someone else to fix theirs with.
Be much gentler than I was, and be sure to use a flathead to press the little tabs in on the bottom and not just press them in with your fingers and wiggle the bottom panel to get it loose.