On the question of 'abandoned' neighbourhood areas, there are several
in London. They are referred to by as neighbourhoodplanners.london as
'orphan areas'. Most result from the local authority resisting the
boundary that was applied for and amending it to such an extent that
no forum subsequently wanted to progress to a plan. Or from local
authorities 'refusing' the forum part of a designation application, on
questionable grounds. leaving the area 'orphaned'.
This has happened on two occasions as a result of deisgnation
applications to LB Hammersmith & Fulham, resulting in an unnamed
neighbourhood area at Eynham Road W12 and another one at the Old Oak
Estate, south of Wormwwod Scrubs.
So it does seem unclear whether such areas remain in a ghost-like
limbo, or expire after five years as would a forum which does not
apply for re-designation. Other may have found a relevant piece of
the legislattion.
On the original question of what constitutes 'changing the nature of
a plan' the content of the NPPG does not seem precise. I have not
come across enough examples of second edition NPs to know where a line
is drawn.