Yes, you can filter the starred slug using the bp_get_messages_starred_slug filter. Unfortunately, the ‘sentbox’ slug is not currently customizable.

Here’s an example of how you might filter the starred slug:

add_filter( 'bp_get_messages_starred_slug', 'bp_codex_filter_starred_slug' );
function bp_codex_filter_starred_slug( $slug )…[Read more]