> If somehow to members of this relation can be reverted to
back when there were 400 members, then that would be good.
Given that the original change happened in March 2019, no-one's
going to be able to "wave a magic wand" and restore this relation
to back how it was then, since there will be ways that existed
then that don't exist any more. However the restore is done there
will be quite a lot of "manually filling in gaps" needed.
Are you asking the list because you'd like to check that it is a
good idea, because you'd like to do it yourself but don't know
how, or simply don't have time to do it yourself and just wanted
to make more people aware of the problem? All of these perfectly
valid reasons of course.
If I was going to do it I'd probably start by undoing the
relation back to the changeset 67822240 version with "undo.pl"
from the perl revert scripts, and then fill in the gaps manually
by looking at http://overpass-turbo.eu/s/10rc (that's an overpass
query of that relation on a date just after the last "valid"
change). However, there may be quite a few gaps to fill in, so
it'd likely need someone with a bit of free time to do that part
(which depending on the answer to the previous question, may or
may not be you).