Change Name of Category Heading in New Post

You can handle the wp_taxonomies object during init action. Then you can change the default labels for the categories and posts tags.

function wpse292282_rename_default_taxonomies() {
    global $wp_taxonomies;

    // Update datas for Category
    $labels = &$wp_taxonomies['category']->labels;
    $labels->name="Sector";
    $labels->singular_name="Sector";
    $labels->add_new = 'Add Sector';
    $labels->add_new_item = 'Add Sector';
    $labels->edit_item = 'Edit Sector';
    $labels->new_item = 'Sector';
    $labels->view_item = 'View Sector';
    $labels->search_items="Search Sectors";
    $labels->not_found = 'No Sectors found';
    $labels->not_found_in_trash="No Sectors found in Trash";
    $labels->all_items="All Sectors";
    $labels->menu_name="Sector";
    $labels->name_admin_bar="Sector";

       // Update datas for Tags
    $labels = &$wp_taxonomies['post_tag']->labels;
    $labels->name="Technologies";
    $labels->singular_name="Technology";
    $labels->add_new = 'Add Technology';
    $labels->add_new_item = 'Add Technology';
    $labels->edit_item = 'Edit Technology';
    $labels->new_item = 'Technology';
    $labels->view_item = 'View Technology';
    $labels->search_items="Search Technologies";
    $labels->not_found = 'No Technologies found';
    $labels->not_found_in_trash="No Technologies found in Trash";
    $labels->all_items="All Technologies";
    $labels->menu_name="Technologies";
    $labels->name_admin_bar="Technologies";

}
add_action( 'init', 'wpse292282_rename_default_taxonomies' );