Yeah that’s a tough one. I’ve basically created a new theme based on the RTFM skeleton/theme. I think the only way to reliably do this without making breaking changes is to use the theme inheritance and create a child (?) theme to modify the Antimatter theme. http://getgrav.org/blog/theme-development-with-inheritance
Thanks guys. I didn’t saw that blog post. however, I realize that I don’t have to update de themplate. I juste saw I could do it and I did it for no real reason. I’m just used to CMS that have security update each weeks. If I understant correctly: If I don’t update the template but update the core, I won’t have any issue?