my_buddyforms_excerpt_length.php

<?php

function my_buddyforms_excerpt_length($length){
    global $post, $buddyforms;


    if( !isset($post->ID) ){
        return $length;
    }

    // Filter for a specific form
    $form_slug = get_post_meta($post->ID,'_bf_form_slug', true);
    if( isset($form_slug ) && $form_slug == 'post'){
        return 100;
    }

    // Filter for a specific post type.
    if( $post->post_type == 'post'){
        return 50;
    }


    return $length;
}

add_filter('excerpt_length', 'my_buddyforms_excerpt_length');