that doesn't quite work for me. i think that, if all of the dimensionless parameters remain constant,
= 299792458 old_meters/old_second = 299792458 new_meters/new_second
and the new_second cannot be the same as the old_second if the meter had changed.
but i think we (as well as Duff) agree: ain't no operational difference. a change in c
(or in G
or any other sole dimensionful
"constant") is not merely impossible, but is functionally meaningless.
i still don't know what to think of this inflationary universe theory where the universe expands faster than c
at some time in its past.