With enough upgrades, the line between replacement and alteration is kind of thin. It's that old "Axe of My Grandfathers" syndrome.
As to Tech I vs. Tech II class, if I understand correctly what you're looking for, check out this page:
http://en.wikipedia.org/wiki/Spaceships_of_EVE_Online
Frigates / EA Ships or Interceptors
Destroyers / Interdictors
Cruisers / Heavy Interdictors
Battlecruisers / Command ships
Battleships / Marauders
… etc.