Is there code compliant way to attach deck joists below a deck beam (or at least lower than flush with the top of the beam)?
Joist hangers are used all the time to fix joists to the side face of the beam. I see no particular reason that you wouldn't be able to hang the joists even with the bottom of the beam using standard joist hangers like these:

Picture Source
In fact ceiling joists may very well be hung with similar brackets like these where the ceiling height is set to be at the bottom of the support beams.
Hanging your deck joists totally below the beams seems a bit problematic. My guess would be that even if you could come up with some type strapping to securely hold the joists up against the bottom of the beam that an inspector may very well reject the concept, especially if they figure out that you are playing games to work around your railing height restriction.