Yes, if your save works on 9.2 sysnand, that means it's a 6.0+ save. So if you run 9.4 (either sysnand, or emunand), provided it's the same format (no unlinking), then the game will work as if you simply updated your 3DS with no hacks. And, naturally, online will work as it should. I'm not sure what Pokebank's save thing is (if it even matters). But yes, if you upload your pokemon on 9.2/9.4, and then downgrade to 4.X/9.4 it should work. I'm not all that familiar with pokemon, but would reimporting your pokemon work even after you delete the save? Or a similar question: can you use someone else's save game to import/export pokemon to your poke bank? If the answer is yes, then this should work.
1. Stay on 9.2 sysnand and 9.4 emunand, be sure they are linked (so software/saves work on both). Boot up 9.4 emunand (update to it if needed).
2. Transfer pokemon to pokebank. This should work just as if you were on legit 9.4.
3. Delete pokemon save (on 9.2, though it doesn't matter, since they are linked).
4. Downgrade sysnand to 4.5.
5. Boot up 9.4 emunand, and play pokemon, creating a new file.
6. Exit pokemon, enter poke bank and reimport pokemon.
This should in theory work, provided poke bank doesn't have any weird restrictions/problems with the pokemon save game. If I had to wager a guess, there's a chance it might not work if Poke bank is expecting a 6.0+ save.
If you just want to play online, you don't actually need to downgrade. Restarting the save is ONLY necessary if you want to have sysnand 4.X. If you are ALREADY on 9.2, just leave that, and update emunand to 9.4. Then play on emunand like normal. This will work fine for online.
So to be absolutely clear, here are your options:
1. Back up pokemon from your 6.0+ save file, clear the save game, downgrade to 4.X, restart save and import pokemon (reimporting might not work, if it requires a 6.0+ save).
2. Stay on 9.2 sysnand, and update your emunand to 9.4. This will allow you to play pokemon just as usual.
The difference is the end sysnand you will be on. If you end on sysnand 4.X, then you can do 4.X stuff, like CFW. But all of your saves MUST be in 4.X saves (rather than 6.0+) otherwise they won't load (you can get around this by having a gateway and running classic mode, that will load your 6.0+ saves). If you end on sysnand 9.2, your 4.X saves for 6.0+ games won't work. Which if you have been playing legit retail games and are on 9.2, this shouldn't be a problem.
Hopefully this all makes sense. It just depends on your goal. Your pokemon save will work as long as your are above 6.0 sysnand. Or are using gateway classic mode (WITH a gateway cartridge).
Your 6.0+ games WON'T work if you are IN (currently loaded) 4.X sysnand. To play them, you'd need to boot into 9.4 emunand. Alternatively, if you stay on 9.2 sysnand, they WILL work, regardless of whether you are in sysnand or emunand. emunand 9.4 will allow you to play online, while 9.2 sysnand isn't that important, besides ensuring save compatibility WITHOUT a gateway card (with a gateway card it doesn't matter).