It appears that they haven't yet loaded the details of how that journey will be handled, other than indicating that it's impacted. (I'm basing this off the "The changes to Greater Anglia are not currently shown in the National Rail Enquiries Journey Planner, please check back nearer to the time of travel." bit at the bottom.) I'd wait until closer to the date to find out exactly what's going on and what alternative plans they've made for those with tickets for that service. Most likely they'll offer a bus from London Liverpool Street to wherever trains are actually running, as it appears that most of the route you'll be on should not be impacted

Oh, it's London Liverpool Street. Referring to "Liverpool Station" might make someone think that you're boarding a train to/from Liverpool.