To customise the Genesis loop on the blog page only, the blog page can be conditionally selected,  the loop removed on that page only and a custom loop inserted.

The blog page is selected with is_home, the genesis_do_loop is removed and a new loop wpb_change_home_loop is inserted.

The core markup for the genesis_do_loop is found in the framework at /lib/structure/loops.php line 75 genesis_standard_loop, so here you can adjust what is needed to output.

In the example above the excerpt is removed genesis_entry_content, but re-added with the_excerpt_max_charlength which refers to a separate function below the loop function to alter the character count of the excerpt – set to 200 in the example, also since the featured image is removed by genesis_entry_content this is also added back in with genesis_do_post_image.