I've had to deal with this too. It's tricky, because when I've tried to correct some people with more realistic expectations, I've been told I'm being pessimistic and that I need to have a more positive attitude, that I shouldn't be having the surgery then, etc. Some people I knew better than to say anything to. I think it's easier to just wait until after you have the SCS in and you know that it's working for you, because then you have objective data to say "it's giving me a lot of pain relief, it's reduced my pain by this%, I can now do these things that I couldn't do before, I'm on lower doses of medication...", and whatever kind of benefits you get from it. If there are some people though that you feel you can have a logical conversation with, I'd say you can go ahead and tell them now. I'm 22 and I found that my friends, younger adults, understood the realistic aspects of what it would give me a lot better than older adults on average. But that's just my personal experience.

Good luck with however you deal with people, I know it's hard. They have good intentions and they're trying to be helpful, but unless someone goes to the doctor's appointments and hears everything you hear it can be hard for them to understand.