Can I replace piston rings only on one piston on a ford ranger 2.3 it had blown head gasket and it was the only affected piston. Or?

Will i see trouble from that cylinder having higher compression then others?

Since you are taking off the head and the sump, its only a small extra effort to do all the rings isn't it?
Might just as well do it while you're in there, I would.

I would also de-coke the head, re-seat the valves, de-gunk the sump (checking for any swarf) and I would check the bearing shells - since I was in there anyway.

But thats what I would do, if I were about to embark on the job you have set yourself.

Hi so here is the facts of life with engines. If has damage to one piston it must have an under lining reason why this has happened. So it needs further investigation. The chances are this was a timing belt breakage which has smashed valves up against it. And there's a lot more wrong than just piston rings. Knowledge is a must in such situations.

How many miles on the motor jojo? I've done so many head gaskets I lost count over the last 35 years. I've never had one piston need rings replaced because of a bad head gasket. I'd either put a used motor in it or completely rebuild the motor.

I assume you are trying to keep the cost down, ie don't want to invest more than the vehicle is worth.

My experience: had an older vehicle, big V8, about 65,000 miles on it when a piston fractured. Pulled the heads: no damage to heads, cylinder was not badly scored. SO: we replaced one piston with a new one and buttoned it all back up. Did a compression test after it was worn-in: well within specs. Kept the thing another 10 years!

You physically can change 1 piston's rings but why would you? 99% of the work to do 1 has been done to do all the others, do it once, do it right