LNER’s journey planner seems to suggest the latter option via London, Leicester, Nuneaton and Manchester is.
Yes, there is a short-term easement as described here
https://www.railforums.co.uk/threads/national-routeing-guide-update.99396/page-51#post-6109446
701064 (Map) Due to engineering closures south of Milton Keynes from 07 April 2023 to 10 April 2023. This map easement will allow journey planners to show itineraries using rail replacement services and onward train journeys from Kettering and Bedford to London St Pancras International. It will apply in both directions.Over Easter, there are line closures between Milton Keynes and London Euston, and also between Bletchley and Bedford. The extent of the closure varies day to day.
This easement adds Rugby, Kettering, Bedford, West Hampstead Thameslink and London St Pancras to any mapped routes which need them.
Therefore, journeys via Kettering are valid on 9 April. Note that the Hope Valley line is shut, so going via Sheffield isn't straightforward.
Thanks, had not considered the via Reading & Manchester route. Would an off peak return be valid. My actual ticket is an off peak return from Chelmsford to Liverpool.
There are permitted routes from London to Liverpool via Reading and via Manchester, but technically not one which includes both. However, I think that the following itinerary would be fine (although the cross-London transit is tighter than required), effectively 'switching routes' in Birmingham.
0715 Chelmsford to London Liverpool Street 0758
0807 Liverpool Street to Paddington 0825 (Circle Line)
0833 London Paddington to Reading 0857
0915 Reading to Manchester Piccadilly 1230
1323 Manchester Victoria to Liverpool Lime Street 1401
The 0843 from London Paddington arrives in Reading at 0910 so may also be possible, but is under the required connection time at Reading.
It looks to me that the latter train could also be picked up travelling via St Pancras, Leicester and Nuneaton, with a later departure from London (0903 or 0930), provided transit between Piccadilly and Victoria was quick. Unfortunately closure of the Hope Valley means no quick trains via Warrington Central on that day.
One other option is to go via Shrewsbury - permitted on route combination ME+RB+RG via Reading.
0715 Chelmsford to London Liverpool Street 0758
0807 Liverpool Street to Paddington 0825 (Circle Line)
0833 London Paddington to Reading 0857
0915 Reading to Wolverhampton 1118
1141 Wolverhampton to Chester 1319
1330 Chester to Liverpool Lime Street 1413