Making radical changes to any process will damage a company, sometimes beyond a point that will allow the company survive. The key to implementing lean systems is to a) understand your starting point and b) make the changes gradually.
In my company I have seen lean implemented in a number of areas (including overhaul) and while it hasn't been smooth it has brought about benefits. It's a long road to transform an organisation with alot of history behind it but if the changes are implemented in gradual steps it can make the place alot better to work in i.e. not always fire-fighting problems.
Cheers,
P2C