Cisco managed to unmanaged

Why would you want to do this?

Not really.  I mean you could always change the passwords by closing your eyes and then typing in something random so you have no clue what it is.  Then in order to do anything to it, you would need to use the password recovery steps.

our client is under the impression that all of there managed switches were at one point unmanaged.  if a switch failed they could just replace it with another one and not load any configurations in to it.

foochar is correct.  If you put no configuration on the switch at all, they are "plug and play."

However, if you are not going to use any of the extra features that a managed switch gets you, then save money and by unmanged switches.

However with unmanged switches you loose things.  In addition to no VLANs, you also can't monitor for port traffic utilization, you can't mirror ports for sniffing traffic, no Etherchannels to add bandwidth between switches, and probably a few other things.

And another big difference in unmanaged switches is no spanning-tree.  So loops can create... interesting events.