Hi!
Hm.... interesting question. It made me think to create a way on the Class Curve plugin to not mess with the default parameters. But don't know when I will be able to do that.
Well, alternativelly, what you can do is find a "level up common event" plugin. That everytime an actor levels up, a common event is played.
So in that common event, you can raise the Custom Parameters the way you want with the plugin commands or script calls provided into the help file.