Trying to serialize one custom capability, not all data. (Or how to make certain data readable to other mods)

So I'm creating a mod, and trying to get this mod compatible with another mod called "Figura". It's a model creation mod and one of the neat things it lets you do is use the player's NBT data in your models. Originally I thought since my the stuff I wanted to be used was a capability it was all good, then I realized that it never saved to NBT in a way I wanted it to. I tried to forcefully save it using event.player.serializeNBT();, but the discovered that saves everything at the exact state, and unless your calling it very slowly it effectively freezes every stat in the game.
There's also some way to create a plugin for figure, but there's no documentation and I don't know how to even let a plugin see the data I want it to see from my own mod. 

If someone could answer either question, that would manage to solve my problem!