First off, I’m a little confused by this question because to my knowledge, nothing should have changed. I could be wrong, but I’m looking everything over and while things have been moved, it’s all the same. You’ve got the same array with the same filter.
The editing framework functions tutorial you’re looking for is here, but it shouldn’t matter in this case. You should be able to do this simply with filters. You don’t need to edit any functions.
Both of what you’re doing are right as far as I can tell. However, if you’re adding the filter from your Child theme’s functions.php, I’d assume it’s getting overridden by the theme’s filter on slider image sizes. But that should have been the case before you updated, also. To combat that, you’d give your filter a priority. — http://codex.wordpress.org/Function_Reference/add_filter
Or, you can include the framework at the top of your Child theme’s functions.php as allowed starting with framework v2.1 and simply place all of your filters after that. See the child theme example’s functions.php that now comes with the new theme package for what I’m referring to.
But you shouldn’t be getting a PHP errors from what you’re doing. What is the PHP error you’re getting? When there’s an error, it’s always helpful to read it, as it generally tells you what the issue is. 😉