How to edit Vanilla attribute limits?

Hi!

I've been working on a mod recently over the past 5 months going over an adventure after the Ender Dragon. I've been constructing a boss mob but there is one problem: The maximum health limit is set to 1024. So my boss mob can't go over this limit. I could use some type of resistance but i don't like this idea. Does anybody know how to change vanilla attributes? 

Thanks.