You could. It would require a few changes, but nothing too complicated. Here’s a list of lines where you’d need to change “post” to “recipe”, assuming you’ve already set up your recipe post type.
meta_box.php lines 9 and 363
taxonomies.php lines 36,67,98,129,186,187,188,189
In widgets.php after line 102 in the post query $args array, you’d need to add this: 'post_type' => 'recipe',
You shouldn’t lose the recipes you’ve added to posts, either. The output filter will still run over the_content and check for recipe data and output the recipe box if it finds it.
That should pretty much do it. You will lose all your changes if you upgrade with future updates, so just keep that in mind. I also can’t support this, so this is “at your own risk’.