‘today’ & ‘tomorrow’ on group listings

You can use the wpt_listing_group_day filter to manipulate the output. See:
https://github.com/slimndap/wp-theatre/blob/master/functions/wpt_events.php#L428

Here is an (untested) snippets that does this:
https://gist.github.com/slimndap/f929599e8dc7311bc0e5bf74ad17f155

You can add it to the functions.php of your theme. Be sure to make a backup before you make any changes.