A correspondent (Thanks, David.) reports a notice at Huyton warning that the Up Chat Moss Slow (Roby and Huyton platform 4.) overhead should be treated as live from 12:00 Sunday 8 October.
That doesn't leave much time for testing, as the first train along there is due at 0629 on Monday morning.
(I'm assuming all the track changes will be complete by then, in which case trains for the Up St Helens line will have to use platform 4.)