Leandro

I do not believe that there is a good way to achieve what you want on the router. It is not difficult to change the privilege level of the show running-config command. But the way that IOS works when you lower the privilege level of show running-config people can execute it but they will not see configuration lines which they do not have privilege level to modify. So these users would see very little of the actual config.

Perhaps it might be possible to store the router config files on some server and to grant read only access to them on that server?

HTH

Rick