With the Experience-Scriptexp.js it's possible to customize when a pet will level up. As you can see at the file ending, the used language is JavaScript.
Installation
1.
Download Rhino, rename the jar to rhino.jar and put the file into the MyPet folder.
2.
Set LevelSystem.CalculationMode to JavaScript int the config.yml.
3.
Edit the exp.js to your likings.
Script
To make a fully functional exp-script that can be used by MyPet you have to implement the following method: