The limit of 7 hops in a switched network with STP enabled is a physical limit or may I have more than 7 hops simply by adjusting the max age and forward delay parameters?
the diameter is an option of the spanning-tree root macro that is executed only once: it should be the same as adding a new switch with a lowest priority: it takes over the root brdige role over the one that was configured with spanning-tree root (there is usually an advice about this)
The changes have to be done on the root bridge: they should be not effective if done on a non root bridge that uses the timers that are in the STP BDPU originated by the root.
