Originally Posted by Bobsled
is it possible to install the cogs of the cassette (ultegra) backward
Not without grinding one of the tabs on the cogs (the wider one).
History note: You could flip Uniglide cogs (except those with built in spacers) since the splines were symmetrical. The tooth profile was also symmetrical so it worked the same either way. You could get twice the life out of a cassette!