Hi there!
I can't give you the information at this moment as I don't have the source here, but a new update is planned that will support LUA + custom scripting and will allow you to write your own JSON exporter. It'll be launched on Juice FX first and then on Pixel FX Designer, you can check the documentation (of Juice FX's one) here: http://codemanu.pro/juicefx
I'll try to give you more info about the .JSON export as soon as possible., although I recommend you to join the app's discord as I'm more active there for this kind of questions. https://discord.gg/azdqRf8