Yep, totally possible to add more bars! You'll have to create new variables in the same pattern that the Hunger/Thirst ones follow, and add new Pictures for the extra bar.
Viewing post in Can I add a third bar?
I've figured most of it out and edited one of the fill bars to make a third one; but I don't know how to get the third bar to work properly. Right now, it seems to start as a small line at the front of the third main bar and then grows backwards. I feel like it has to be something wrong with the new variable because i tried linking it to the current thirst variable instead of the new current energy variable and it showed up in the right spot. I'm not really sure how to fix it.