No stations or lines closed at all, but...
Reduce frequency off peak on a number of inter-city routes to free up capacity and paths. Compensate by making trains longer where possible.
Three specific examples:
Euston to Birmingham and Manchester reduced to 30 mins off peak, to allow 30 min clockface service on Cov-NS and Stockport-Manchester corridors and de-congest the railway. There would still be three trains an hour in the peak on each route, using the two off peak paths and a third path unused off peak.
Return the MML to the old pattern of two fasts and two semi-fasts an hour, the fast overtaking the semi-fast at Leicester. Alternate Sheffield and Nottingham endpoints for each.
This next one would only be possible by returning to BR or combining Chiltern, GWR and XC into one TOC, but anyway.... rationalise (by removing perhaps duplicate services), but at the same time, improve the total capacity, on the Reading-Birmingham corridor. Firstly run all Bournemouth-Manchesters with at least 8 coaches, and 12 at busy times, north of Reading. Divert one Marylebone-Birmingham an hour to Paddington (via Reading and Oxford) and New Street (via Solihull as now), providing both the second Paddington to Oxford an hour (in addition to the Worcester) and the second Reading to Birmingham (in addition to the Bournemouth). Both services (the retained Marylebone and this new service) to be 12 coaches. 8 coaches of this new Paddington to New Street to continue north of Birmingham as an XC-style service as now.
Ensure all three services are timed to provide even interval services between Reading-Birmingham, London-Oxford and London-Banbury/Leamington.
This would mean 32-36 coaches an hour between Banbury and Leamington on fast services vice around 20 now; 20 to 24 between Reading and Birmingham vice 10 max now; and 24 between Leamington and London (vice around 10 now).
Also <duck> return Thameslink to its 1988 state. It seems the introduction of the new timetable has caused no end of problems and has caused 'classic' services into the termini to suffer as a result. Maintain high frequency on the core by running a London Bridge-St Pancras high frequency shuttle.