How to change ‘Move to Trash’ to ‘Move to Draft’ for my blog’s users?

You can use add_filter() for post_row_actions to filter out the ones you don’t want, add in the functions you do want. Like so:

<?php
/** Plugin Name: (wpse) Draft vs. Trash Posts */
add_filter( 'post_row_actions', 'my_plugin_update_actions', 10, 2 );
function my_plugin_update_actions($actions, $post) {

    $capability = 'promote_users';
    $role="Administrator";
    // Choose what you want to check against. Better only use one: Capability *or* role.
    if (
        current_user_can( $capability )
        OR current_user_has_role( $role )
    ) {
        unset($actions['trash']);
        $actions['draft'] = '<a class="submitdelete" title="Move this item to drafts" href="'.admin_url('post.php?post=".$post->ID."&action=draft').'">Move To Draft</a>';
    }

    return $actions;
}

That should get you started in the right direction.